depression as a prognostic factor of lumbar spinal stenosis: a systematic review

The Spine Journal 14 (2014) 837–846

Review Article

Depression as a prognostic factor of lumbar spinal stenosis:a systematic review

Ashley B. McKillop, BSca, Linda J. Carroll, PhDb, Michele C. Batti�e, PhDc,*aFaculty of Rehabilitation Medicine, University of Alberta, 8205 114 St, Edmonton, AB T6G 2G4, Canada

bDepartment of Public Health Sciences, School of Public Health, University of Alberta, 3-300 Edmonton Clinic Health Academy, 11405 – 87 Ave,

Edmonton, AB T6G 1C9, CanadacDepartment of Physical Therapy, 2-50 Corbett Hall, University of Alberta, Edmonton, AB T6G 2G4, Canada

Received 17 January 2013; revised 12 September 2013; accepted 27 September 2013

Abstract BACKGROUND CONTEXT: The clinical sy

FDA device/drug

Author disclosure

(B, Paid directly to in

to disclose.

The disclosure key

TheSpineJournalOnlin

Supported by the

Health Solutions.

* Corresponding a

Rehabilitation Medici

ton, AB T6G 2G4, C

E-mail address: m

1529-9430/$ - see fro

http://dx.doi.org/10.10

ndrome of lumbar spinal stenosis (LSS) is a com-monly diagnosed lumbar condition associated with pain and disability. Psychological factors, in-cluding depression, also affect these and other health-related outcomes. Yet, the prognostic valueof depression specifically in the context of LSS is unclear.PURPOSE: The aim of this systematic review was to examine the literature on depression as aprognostic factor of outcomes in patients with LSS.STUDY DESIGN: Best-evidence synthesis.PATIENT SAMPLE: Patients receiving the diagnosis of LSS and surgery.METHODS: A best-evidence synthesis was conducted, including articles published between 1980and May 2012. Each article meeting inclusion criteria, including a longitudinal design, was crit-ically appraised on its methodological quality by two authors independently, who then met to reachconsensus. Only studies deemed scientifically admissible were included in the review.RESULTS: Among the 20 articles that met the inclusion criteria, 13 were judged scientifically ad-missible. The evidence supports an association between preoperative depression and postoperativeLSS-related symptom severity (a combination of pain, numbness, weakness and balance issues) anddisability. The effect size for these associations was variable, ranging from no effect to a moderateeffect. For example, an increase of 5 points on a 63-point depression scale doubled the odds ofbeing below the median in LSS-related symptom severity at follow-up. Findings on the associationbetween preoperative depression and postoperative pain alone and walking capacity were morevariable.CONCLUSIONS: Findings support that preoperative depression is likely a prognostic factor forpostoperative LSS-related symptom severity and disability at various follow-up points. The prog-nostic value of depression on the outcomes of pain and walking capacity is less clear. Nonetheless,depression should be considered in the clinical care of this population. � 2014 Elsevier Inc. Allrights reserved.

Keywords: Depression; Spinal stenosis; Psychosocial factors; Prognostic factor; Systematic review; Best evidence synthesis

status: Not applicable.

s: ABM: Grant: Alberta Innovates Health Solutions

stitution). LJC: Nothing to disclose. MCB: Nothing

can be found on the Table of Contents and at www.

e.com.

Canada Research Chairs Program, Alberta Innovates

uthor. Department of Physical Therapy, Faculty of

ne, University of Alberta, 2-50 Corbett Hall, Edmon-

anada. Tel.: (780) 492-5968; fax: (780) 492-1626.

[email protected] (M.C. Batti�e)

nt matter � 2014 Elsevier Inc. All rights reserved.

16/j.spinee.2013.09.052

Introduction

The clinical syndrome of lumbar spinal stenosis (LSS) is apainful condition that negatively influences many health out-comes, such as disability, walking capacity, and quality oflife [1–4]. Psychological factors also have been shown to af-fect these and other health-related outcomes. Slover et al. [5]found in patients who underwent lumbar spine surgery thatdepression was one of the comorbidities most associated withpoorer recovery of physical function, as indicated by thephysical component summary score of the Short-Form 36.

Delta:1_given name

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Delta:1_given name

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mailto:[email protected]

http://dx.doi.org/10.1016/j.spinee.2013.09.052


Figure. Results of article search and selection.

838 A.B. McKillop et al. / The Spine Journal 14 (2014) 837–846

Depression and pain conditions, including back pain andother pain conditions, frequently coexist and when occur-ring together, are associated with greater pain severity,poorer health-related quality of life, and increased disabil-ity [6,7]. The relationship between depression and pain iscomplex and most likely bidirectional. In a systematic re-view of psychological risk factors in back and neck painit was found that of 16 studies, 14 showed that depressedmood increased the risk for the development of pain condi-tions [8], whereas in a subsequent study [7] the strongestpredictor of depression was back pain. In regard to the viewthat depression is a risk factor for chronic pain, it has beennoted that the supporting literature has significant limita-tions; for example, the precise onset of pain has not beenidentified in some studies, which precludes concluding thatdepression triggered the pain [9]. Nonetheless, it is impor-tant to understand the direction and magnitude of this rela-tionship when considering strategies to improve patients’treatment and recovery.

Although reviews of prognostic factors in low back painhave suggested that depressed mood may increase the riskof chronicity [10] and costs to health care [11], such evi-dence may not generalize to an LSS context. Recent find-ings indicate that patients diagnosed with LSS havepoorer health-related quality of life and increased comor-bidities compared with persons of similar age sufferingfrom chronic back pain [4]. It is also possible that othersymptoms specific to LSS, such as neurogenic claudication,could contribute to an increased burden of illness in pa-tients with LSS. This suggests that the burden of illness,and possibly associated psychological factors and their ef-fects, in patients diagnosed with LSS are distinct fromthose with chronic back pain in general. The purpose of thissystematic review is to examine the evidence on depressionas a prognostic factor of LSS outcomes.

Methods

Search strategy

The search strategy was developed through consultingwith both a library scientist with experience in systematicreviews and other content experts to select appropriatesearch terms. The search strategy included synonyms of rel-evant terms related to LSS and depression to help ensure allarticles were found (eg, search strategy for MEDLINE canbe found in Supplementary Appendix A).

We systematically searched the following electronic li-brary databases (Figure): Scopus, Web of Science, CINAHL,MEDLINE, WorldCat, Cochrane Library, EMBR Reviews,and REHABdata. In an attempt to locate any articles thatmay have been missed in the initial search, we also exam-ined reference lists of all articles identified as relevant.

Electronic library databases were searched for articlespublished from 1980 through May 2012. We chose 1980

as the earliest publishing year of the search term, as beforethis there was limited research that considered the effect ofpsychosocial factors in the context of LSS. Indeed, whenwe entered the same search strategy within MEDLINEbut limited the search between 1950 and 1980, no relevantarticles were yielded.

Study selection

After studies identified in the search were uploaded in-to reference managing software, citations were assessedby the first author to determine whether they met the in-clusion criteria by first reviewing titles and abstracts andthen reviewing full texts of articles judged to be poten-tially relevant. At this stage of the review, the methodo-logic quality of the study was not considered. The sameauthor conducted this screening process on two separateoccasions to minimize the possibility that articles weremisclassified.

The inclusion criteria used for screening for relevancewere as follows:

1. Studies reporting original data.2. Studies reporting findings related to depression as a

prognostic factor of an LSS outcome.

a. Studies that described depression with alternativeterms but clearly stated the method of assessing de-pression or depressive symptomatology (eg, depressivesymptomatology assessed with Center for Epide-miologic Depression Scale) were included.

62years

[21]

62years

[21]

1.86(95%

CI0.72-4.81)*

[18]

62years

[21]

62years

[21]

1.60(95%

CI0.57-4.48)*

[18]

62years

[21]

62years

[21]

839A.B. McKillop et al. / The Spine Journal 14 (2014) 837–846

b. Studies that included subjects with a diagnosis ofLSS.

c. Studies of mixed samples in which patients diag-nosed with LSS were not separated from other lowback problems in the analysis were excluded.

3. Use of a longitudinal study design. (Cross-sectionalstudies, single case reports, opinion papers, narra-tive reviews, letters to the editor, or editorials wereexcluded.)

4. Articles published in English from 1980 throughMay, 2012.

5. Studies using human participants.

Table

1

Effectestimates

ofpreoperativedepressiononpostoperativeoutcomes

Outcome

Follow

-uptime

3-m

onth

6-m

onth

1-year

2-year

LSS-related

symptom

severity

Oddsratio

1.16(95%

CI1.02–1.31)[22]–

1.15(95%

CI1.03–1.29)[20]1.20(95%

CI1.06–1.35)[19]

Coefficient

––

–2.30[26]

Disability

Oddsratio

1.19(95%

CI1.05–1.36)[22]–

1.15(95%

CI1.03–1.29)[20]1.17(95%

CI1.05–1.30)[19]1.08(95%

CI0.92–1.26)!

1.20(95%

CI1.01–1.43)$

Coefficient

––

�0.02(SE:60.2)[29]

0.03(SE:60.20)[29]

�2.01[27]

Pain(alone)

Oddsratio

1.13(95%

CI1.00–1.27)[22]–

1.06(95%

CI0.97–1.16)[20]0.95(95%

CI0.88–1.04)[19]0.94(95%

CI0.82–1.06)!

0.96(95%

CI0.83–1.10)$

Coefficient

–0.53(SE:

60.18)

[28]

––

Walkingcapacity

Oddsratio

1.06(95%

CI0.95–1.19)[22]–

1.19(95%

CI1.05–1.35)[20]1.10(95%

CI1.00–1.20)[19]1.14(95%

CI0.96–1.35)!

1.01(95%

CI0.88–1.17)$

Coefficient

––

––

CI,confidence

interval;LSS,lumbar

spinal

stenosis;SE,standarderror.

Depressionwas

analyzed

asacontinuousvariable

exceptwhen

notedbyan

asterisk,when

itwas

dichotomized.

Quality assessment

All three authors of the current study served as reviewersand worked in pairs. Each article deemed relevant was crit-ically appraised by two reviewers independently with a crit-ical review form adapted from the Qu�ebec Task Force onWhiplash-Associated Disorders [12,13] and used in subse-quent systematic reviews on a variety of health topics (c.f.[12,14,15]). These forms were designed to guide the re-viewers in evaluating the presence and likely effects of se-lection bias, measurement errors, and measurement bias,confounding and adequacy of statistical analysis.

At the end of the review form, each reviewer was askedto judge whether the study was scientifically admissible. Astudy was judged scientifically inadmissible if methodo-logic flaws and biases were likely to have compromisedthe internal validity of the study. A study was deemed sci-entifically admissible if both reviewers agreed that themethodology was sufficiently sound (eg, reasonable val-idity) to have confidence in the findings. Discrepanciesbetween the independent reviewers’ conclusions wereresolved through discussion, with the addition of a thirdreviewer when consensus was not reached in these discus-sions. As per best evidence synthesis methodology, allstudies judged to be scientifically admissible were in-cluded in the evidence tables [16,17].

Data collection

The first author extracted data relevant to the researchquestion from the articles deemed scientifically admissibleand recorded these in evidence tables. Data in the evidencetables were then reviewed by the two coauthors for accuracy.The principle summary measures recorded were odds ratios(ORs), regression coefficients, spearman correlation coeffi-cients and confidence intervals. Only the findings from themultivariable analyses were included in the evidence tables,primarily because of space limitations. Also, as one study di-chotomized the same outcome variable in two ways, we onlyreported the findings that were dichotomized by less than a30% outcome score decrease from baseline, as we judgedthis to be most clinically relevant [18].


All reported effect estimates of preoperative depres-sion on postoperative outcomes (ORs and coefficients)from multivariable analyses were placed in a table toaid in interpreting the strength of the observed associa-tions (Table 1).

Results

Selection of studies

The review process is summarized in a flow diagram inthe Figure. The databases yielded a total of 4,733 results.The majority of the articles came from Scopus, Web of Sci-ence, CINAHL, and MEDLINE. After eliminating dupli-cates, the databases yielded 3,670 unique articles. Of thesecitations, 17 were relevant in accordance with our inclusioncriteria. We also identified an additional three articles thatmet the inclusion criteria after screening articles’ referencelists.

Upon conclusion of the critical review of the 20 articles,13 were judged to be scientifically admissible and includedin the best-evidence synthesis [18–30]. Among these 13articles, there were five unique cohorts. Seven of these ar-ticles used data from one unique cohort (Table 2) [18–24].Seven studies were judged to be scientifically inadmissiblebecause of identified weaknesses that taken together wouldlikely result in poor internal validity (confounding bias, se-lection bias, and measurement bias). Examples of identifiedweaknesses in studies deemed nonadmissible were selectiveresponding [31], insufficient sample size for the multivari-able models employed [32–35], use of nonvalidated depres-sion measures [31,35], and insufficient information reportedin results [36] or methods [37]. Inadmissible studies typi-cally were found to have more than one major methodologicflaw. In three articles we accepted part of the authors’ find-ings [19–21]. The remaining findings were not included inthe synthesis because of the use of unvalidated measuresof depression.

Meta-analysis considerations

No attempt was made to pool the data because of insuf-ficient data and as an alternative, we reported all estimatesof the effects in Table 1.

LSS-related symptom severity

All studies examining preoperative depression as a pre-dictor of LSS-related symptom severity measured with thequestionnaire devised by Stucki yielded statistically signif-icant associations. This questionnaire is also known as theSwiss Spinal Stenosis Questionnaire [38]. Preoperative de-pression was associated with greater LSS symptom severityat 3-month [22], 1-year [20] and 2-year follow-up [19,26]in four articles in two unique cohorts. There was also a sig-nificant association between depression at 3 months after

surgery and LSS symptom severity at 2 years postsurgery[23]. There were both adjusted ORs, ranging from 1.15 to1.20 and a coefficient of 2.30 reported for this outcome.For example, an OR of 1.16 would mean that for every1-point increase on the 63-point Beck Depression Inven-tory, the odds of a poor outcome would increase by 16%,and a coefficient of 2.30 would mean for every 1-pointincrease on the 5-point depression scale, LSS symptom se-verity would increase by 2.30 points on a scale standardizedto a range of 0 to 100 (Table 1).

Disability

There were eight articles from three unique cohorts thatused the Oswestry Disability Index, a self-report measureof back-related disability, as an outcome. Statistically sig-nificant associations between greater preoperative depres-sion and greater postoperative disability were reported inall studies [18–23,27], with the exception of Ng et al.[29]. In two cohorts, preoperative depression was foundto predict disability at 3-month [22], 1-year [20] and 2-year [18,19,21,27] follow-up (Table 2). Also, depressionmeasured postoperatively at 3 months [18,23], 6 months[18], and 1-year [18] predicted disability at 2-year follow-up. The statistically significant adjusted ORs ranged from1.15 to 4.94 depending on whether depression was includedin the model as a continuous variable (where an OR of1.15 means that for each 1-point increase in the 63-pointdepression scale, the odds of disability, dichotomized atthe median, increased by 15%) or as a dichotomized varia-ble (where an OR of 4.94 means that presence of depres-sion increased the odds of disability, dichotomized as thepresence or absence of a 30% decrease from baseline, by494%; Table 1). One of the aforementioned articles did aspecific analysis by age, separating older ($62 years) fromyounger patients, and found a statistically significant asso-ciation between baseline depression and disability atfollow-up in older patients with stenosis, but not for young-er patients [21]. However, this study should be interpretedwith caution, as it is possible that the sample size was toosmall for the statistical analysis. When this occurs, themodel is said to be ‘‘overfit,’’ which may result in the mod-el being biased, for example, describing random error,rather than an underlying association between the predictorand the outcome.

Pain

There were six articles from two unique cohorts that ex-amined pain as an outcome. These articles assessed painwith a Visual Analogue Scale [18–22] or a 6-point ordinalscale [28]. Results were mixed; preoperative depressionpredicted pain at 3-month [22] and 6-month [28] follow-up but not at 1-year follow-up [20] (Table 2). In other stud-ies of the same cohort, no association was found betweenpreoperative depression, entered as a continuous variable,

Table 2

Evidence table

Citation Patient characteristics

Patients enrolled and

follow-up periods (n) Depression measure

Outcome (dichotomized or

continuous, measurement)

Relevant findings

(multivariable analysis)

Sinikallio et al.,

2011 [19]

Surgical cases, selection for

surgery (by an orthopedist or

neurosurgeon) occurred between

2001 and 2004 at Kuopio

University Hospital, Finland

Patients enrolled (102),

preoperative (100), 3-month

(99), 6-month (?), 1-year (?), and

2-year (96)

BDI (continuous) 2-year disability (dichotomized,

ODI), 2-year pain (dichotomized,

VAS), 2-year symptom severity

(dichotomized, Stucki), and 2-year

walking capacity (dichotomized,

self-report walking capacity)

Baseline BDI score, adjusting for age, sex,

baseline somatic comorbidity, marital status,

symptom severity, ODI and VAS, was

independently associated with ODI

(OR51.17, 95% CI 1.05–1.30, p!.01) and

symptom severity (OR51.20, 95% CI 1.06–

1.35, p!.01) at 2-year follow-up.

Sinikallio et al.,

2010 [18]








(99), 6-month (?), 1-year (?), and

2-year (96)

BDI (dichotomized at

10 or more

indicating presence

of depression)

2-year disability (dichotomized,

ODI) and 2-year pain

(dichotomized, VAS)

BDI score at 3-months (OR52.94, 95% CI

1.06–8.12, p5.04), 6-months (OR54.94, 95%

CI 1.35–18.09, p5.02) and 1-year (OR52.91,

95% CI 0.99–8.53, p5.05), adjusting for age,

sex, marital status, symptom severity and

disability scores, was independently

associated with a #30% decrease in 2-year

ODI score. Also, BDI score at 3-months

(OR53.33, 95% CI 1.13–9.79, p5.03) was

independently associated with a!30%

decrease in 2-year VAS.

Sinikallio et al.,

2009 [20]








(99), and 1-year (95)



VAS), 1-year symptom severity

(dichotomized, Stucki), and 1-year




marital status, preoperative somatic

comorbidity, pain, symptom severity and

disability, was independently associated with

ODI (OR51.15, 95% CI 1.03–1.29, p!.05),


1.29, p!.05) and walking capacity

(OR51.19, 95% CI 1.05–1.35, p!.05) at 1-

year follow-up.

Sinikallio et al.,

2010 [21]








(99), 6-month (97), 1-year (?),

and 2-year (96)



VAS) and 2-year walking capacity

(dichotomized, self-report walking

capacity)

The only significant association occurred in the

elderly group between baseline BDI score and

2-year ODI (OR51.20, 95% CI 1.01–1.43,

p!.05), after adjusting for sex, marital status,

preoperative somatic comorbidity,

preoperative ODI and preoperative VAS.

Sinikallio et al.,

2007 [22]







preoperative (100), and

3-month (99)

BDI (continuous) 3-month disability (dichotomized,

ODI), 3-month pain

(dichotomized, VAS), 3-month

symptom severity (dichotomized,

Stucki) and 3-month walking

capacity (dichotomized, self-

report walking capacity)


marital status, somatic comorbidity, previous

lumbar spine operation, ODI, VAS and

symptom severity, was associated with ODI

(OR51.19, 95% CI 1.05–1.36, p!.01), VAS

(OR51.13, 95% CI 1.00–1.27, p!.05) and


1.31, p!.05) at 3-month follow-up.

(Continued)

841

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al./TheSpineJournal14(2014)837–846

Table 2

(Continued)

Citation Patient characteristics

Patients enrolled and

follow-up periods (n) Depression measure

Outcome (dichotomized or

continuous, measurement)

Relevant findings

(multivariable analysis)

Sinikallio et al.,

2010 [23]








(99), 1-year (?), and 2-year (96).


ODI), 2-year symptom severity

(dichotomized, Stucki) and 2-year



BDI score at 3-months, adjusting for age, sex,

marital status, preoperative somatic

comorbidity, 3-month pain drawings and

3-month VAS, was associated with ODI

(OR51.18, 95% CI51.04–1.34, p!.05) and


1.31, p!.05) at 2-year follow-up.

Sinikallio et al.,

2011 [24]







preoperative (102?), 3-month

(?), and 1-year (97)

BDI (continuous) SOC (dichotomized, 13-item SOC

scale)

BDI score at baseline (OR51.19, 95% CI 1.05–

1.36, p!.01) and 3-month (OR51.44, 95% CI

1.19–1.75, p!.001), adjusting for age, sex,

and preoperative self-reported walking

capacity, ODI and VAS (model 1), and

3-month self-reported walking capacity, ODI

and VAS (model 2), was independently

associated with low SOC at 1-year follow-up.

Adogwa et al.,

2012 [27]

Surgical cases at the Vanderbilt

University Medical Center in

Nashville


preoperative (53), and

2-year (53)

Zung (continuous) 2-year disability (continuous, ODI) An increased baseline Zung score, adjusting for

age, estimated blood loss, intraoperative

blood loss, preoperative ODI, and time

between index and revision surgery, was

independently associated with less

improvement in disability after surgery

(coefficient5�2.01, p5.05).

Katz et al.,

1995 [25]

Surgical cases, four different

referral centers (Brigham and

Women’s Hospital, Beth Israel

Hospital, University of Vermont

and University of Iowa Hospitals

and Clinics).


preoperative (223), and 6-month

(194)

Zung (continuous) 6-month satisfaction (continuous, 7-

item satisfaction scale)

Baseline depression was not significantly

associated with satisfaction.

Katz et al.,

1999 [26]

Surgical cases, four different

referral centers (Brigham and

Women’s Hospital, Beth Israel

Hospital, University of Vermont

and University of Iowa Hospitals

and Clinics) between 1989

and 1993.



(236), and 2-year (199)

3-item depression

scale (continuous)

2-year walking capacity (continuous,

Stucki), 2-year symptom severity

(continuous, Stucki) & 2-year

satisfaction (continuous, Stucki)

Baseline depression, adjusting for better self-

rated health, less cardiovascular comorbidity,

better walking capacity, noninstrumented

fusion and higher income, was independently

associated with symptom severity (standard

beta coefficient52.3, p5.02) and satisfaction

(standard beta coefficient51.9, p5.05).

Iversen et al.,

1998 [28]

Surgical cases, patients were

recruited from four different

hospitals (Brigham andWomen’s

Hospital, Spine Institute of New

England, University of Iowa

Hospitals and Clinics, and Beth

Israel Hospital) between 1989

and 1993.


preoperative (257), and 6-month

(228)

Zung (continuous) 6-month pain (continuous, 6-point

scale)

Higher baseline Zung score, adjusting for

satisfaction with pain relief, improved

physical function, baseline pain and number

of pain relief expectations, was associated

with elevated pain at 6-months

(parameter50.53, standard error50.18,

p5.003).

842

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Nget

al.,

2007[29]

Surgical

cases,recruited

byaspine

specialist’ssurgical

cohort

(surgeryonly

donebysenior

author)

atLeicester

General

Hospital

between1994

and2001.

Patientsenrolled

(100),

preoperative(100),6-w

eek(?),

3-m

onth

(?),6-m

onth

(?),1-year

(100),and2-year(85).

Modified

Zung

(continuous)

1-yearand2-yeardisability

(continuous,ODI)

Baselinedepressionwas

notsignificantly

associated

withdisability.

Herronet

al.,

1986[30]

Surgical

cases(surgerydoneby

author)

between1979and1983.

Patientsenrolled

(57),preoperative

(57)andminim

um

1-year

follow

-up(Average:18months,

range:

12-57months)

(51)

MMPI(continuous)

SurgicalRatingScale(dichotomized,

surgical

ratingscale)

Baselinedepressionwas

notassociated

with

outcomein

thestenosis

group.

BDI,BeckDepressionInventory;CI,confidence

interval;MMPI,MinnesotaMultiphasicPersonalityInventory;ODI,Osw

estryDisabilityIndex;OR,oddsratio;SOC,Sense

ofCoherence;Stucki,Stucki

Symptom

Severity;

VAS,Visual

AnalogueScale;Zung,ZungSelf-RatingDepressionScale.


and pain at 2 years [19,21]. However, there was a significantassociation of depression at 3 months postoperatively, en-tered as a binary variable, with pain at 2-year follow-up [18].

Walking capacity

There were six articles on two unique cohorts that exam-ined walking capacity as an outcome and, with the excep-tion of one analysis in which preoperative depression wasassociated with walking capacity at 1 year [20], none dem-onstrated statistically significant associations with preoper-ative depression in multivariable analyses (Table 2). Thesearticles assessed walking capacity through self-reportmeasures [19–23], including the Stucki questionnaire [26](also known as the Physical Function Scale of the SwissSpinal Stenosis Questionnaire) [38]. Katz et al. [26] founda statistically significant association between preoperativedepression and 2-year walking capacity in a crude analysisbut not in a multivariable analysis. Also, within the samecohort no statistically significant associations were foundbetween preoperative depression and self-reported walkingcapacity at 3-month [22] and 2-year follow-up [19,21].

Other outcomes

There were three other outcomes measured in three sep-arate articles, all with unique cohorts. One article examinedsense of coherence, ‘‘defined as a pervasive and enduringfeeling of inner confidence and an experience of lifeas comprehensible, manageable and meaningful,’’ throughthe 13-item Sense of Coherence Scale (p 783) [24]. This ar-ticle found a statistically significant association betweenboth preoperative and 3-month postoperative depression,and a low sense of coherence postoperatively. Another articlereported no association between preoperative depression andfair, poor, or good surgical outcome at a minimum 1-yearfollow-up, using the Surgical Rating Scale [30]. Finally,one article reported that those with preoperative depressionwere less satisfied at 6 months postoperatively, in the uni-variable analysis only [25], whereas another article withinthe same cohort reported a significant association with satis-faction at 2 years postsurgery [26].

Discussion

In this best-evidence synthesis, after critical appraisal 13articles using five unique cohorts were judged to be scien-tifically admissible. A variety of outcomes were assessedwith self-report measures of disability, pain, LSS-relatedsymptom severity (a combination of pain, numbness, weak-ness and balance issues) and walking capacity being themost common. Among these 13 articles, there was evidencefrom multiple studies that depression is a prognostic factorfor outcomes of LSS-related symptom severity and disabil-ity. The prognostic value of depression for pain alone and


walking capacity was not as consistent across studies andfollow-up periods.

Although preoperative and postoperative depressionwere both assessed in the included studies as prognosticfactors, it may be important to consider them separately.Seeking surgery, in many cases, can be a last resort and pa-tients who are waiting for this major intervention may havepredefined expectations of their surgical outcome. Yet sev-eral months postoperatively, the patient likely, in part,knows whether the surgical intervention was successful ornot, and may have a very different context to view the fu-ture. However, as postoperative depression was only as-sessed in one cohort we will limit our discussion of thesefindings.

Depression as a prognostic factor

Across all follow-up periods, the association betweenpreoperative depression and subsequent LSS-related symp-tom severity and disability remained relatively consistent,apart from the findings of Ng et al. [29] where depressionwas not associated with disability [18–21,23,27,29]. Nget al. [29] and Adogwa et al.’s [27] studies were similarin that both used the same questionnaires, performed simi-lar statistical analysis and had a 2-year follow-up. One pos-sible explanation for these differing findings is that thepopulation studied by Adogwa et al. [27] was of patientswho elected revision surgery, and possibly had worse casesof LSS, unlike the cohort in Ng et al. [29] that had not re-ceived previous surgery at baseline.

Although the association of depression with outcomesof LSS-related symptom severity, as indicated by com-plaints of a combination of neurologic factors, includingnumbness, weakness, balance, and pain issues, remainedrelatively consistent over time, pain alone tended to bemore highly associated with preoperative depression inearly follow-up periods. One consideration related to thisdifference is that the questionnaire devised by Stucki,which measures LSS-related symptom severity, asks pa-tients to rate LSS-related symptoms over the last month[19,20,22,23,26], whereas the other pain measures, namelythe Visual Analogue Scale and a 6-point pain scale, appearto be examining pain over a much shorter time period[18–22,28]. Thus, the latter may be a less-stable outcomemeasure.

Effect size

Although the direction of an association and the statisti-cal significance are helpful in understanding whether de-pression is a prognostic factor and the nature of theassociation with outcomes, knowledge of the size of the ef-fect is critical in judging the importance and clinical signif-icance of the association. Effect size can be gauged byindividually interpreting the regression coefficients andORs extracted, considering the scale and distribution of

the predictor and outcome variables (eg, continuous,10-point scale, etc.). For example, with the OR of 1.19an increase of 10 points on a 63-point depression scale in-creased the odds of disability by 190%. Given that the stat-istically significant associations were consistent across theoutcomes of disability and LSS-related symptom severity,the focus was on interpreting the effect sizes for theseoutcomes. We concluded that the effect of depression onLSS-related symptom severity and disability is variable,ranging from no effect [29] to a moderate effect [19–22,27]. The findings of Adogwa et al. [27] and Sinikallioet al. [19–22] are consistent with the Pincus et al. [10] re-view on low back pain reporting a moderate effect of de-pression on disability and other outcomes, including painand symptom satisfaction.

Limitations

There are important limitations and strengths of the cur-rent literature on which this best-evidence synthesis isbased. Several limitations were present, such as high attri-tion rates, which increase the risk of selection bias [26],suboptimal analysis strategies (eg, stepwise method, whichcan produce biased estimates, especially in the presence ofcollinearity) [26,28,29], and no reporting of variability inthe estimated regression coefficients in the multivariableanalysis [26,27]. One major limitation is that more than halfof the studies used arbitrary and unvalidated cut-off scoresfor the outcome measures and several had inadequate sam-ple sizes for the statistical analyses performed (ie, the studywas underpowered for the analyses), which could have ledto misleading findings [18–24,32]. The use of unvalidatedcut-off scores, as discussed in Kraemer et al. [39], can beespecially problematic as ORs, in particular, are sensitiveto cut-off points. Another limitation is that different poten-tially confounding variables were adjusted in the multivari-able analysis of each unique cohort, which could haveaffected the strength of the associations between depressionand the measured clinical outcomes. Also, because all pa-tient populations were surgical cases, care must be takenin generalizing these findings to nonsurgical cases of LSS.Finally, this best-evidence synthesis is limited as it is onlybased on five unique cohorts. Thus, new studies could sub-stantially affect the conclusions of this review. Among thestrengths of the studies on which the review is based are thatmost articles clearly defined their study populations, hadhigh follow-up rates and sufficient sample size. In addition,the majority used validated questionnaires and appropriateanalysis methods.

There are also some important limitations to considerwith respect to the methods of this review. Only one authorreviewed the titles, abstracts, and articles to determinewhich met the initial inclusion criteria, prior to review,and one author performed the data extraction for the evi-dence table. Although it is possible that articles weremissed, it is unlikely as the screening of the articles was


performed twice and the reference lists of relevant articleswere screened to ensure important articles were identified.Also, the reviewed studies did not always clearly indicatewhich variables were considered in the statistical analyses,and occasionally we made assumptions when extracting re-lated data. In such cases, more than one author reviewed themethodology and consensus was reached. Finally, we onlyassessed English articles in our review and as a result mayhave missed relevant non-English articles.

An important consideration is that depression, the pro-gnostic factor of interest, was measured by self-report mea-surement tools in this review. It was assumed that alloperationalizations of depression were tapping into thesame construct, despite the use of different self-reportmeasures across the included articles. Although it is possi-ble that our findings could have been biased by the differentmeasures [40], we chose not to stratify the conclusions bymeasurement tool, especially given that there were only 5unique cohorts. Nevertheless, scores of the 21-item BeckDepression Inventory (BDI), ranging from 0 to 63, andthe 20-item Zung Self-Rating Depression Scale (Zung),ranging from 20 to 80, are substantially correlated (0.85–0.86) [41], the two most commonly used depression meas-ures in the included studies. Both measures are thought toassess common symptoms, attitudes, and characteristicsof clinical depression, as derived from clinical observations(BDI) or from prior factor analyses in the literature (Zung)[42,43]. The BDI and Zung are widely available on the in-ternet if more details about the specific items on the depres-sion measures are of interest. Given that these measuresinclude somatic items, which may inflate the depressionscore of populations with chronic pain, it is important thatthe cut-off scores used to indicate the presence of depres-sion are validated in the same population [44–46]. In achronic pain context, cut-off scores of 13 and 21 have beensuggested for the BDI and a score of 50 for the Zung[41,45]. In addition, one study used a three-item depressionmeasure, which also appeared to be assessing common de-pressive symptomology [47].

The best methodology of a systematic review has beendebated. One view is that all-relevant literature should beincluded irrespective of methodological quality and valid-ity. This however may not be ideal, as evidence suggeststhat results of meta-analyses are often biased [15,17] andfail to consider the strengths of individual study designs[48]. An alternative method, as adopted in this review, isassessing the quality of each article and synthesizing find-ings only from those studies that have reasonable methodsand validity [12,13,15–17,49,50]. Another controversialtopic is the criteria for the diagnosis of LSS. Althoughthe inclusion criteria included a diagnosis of LSS, all pa-tients met the current criteria outlined by the North Amer-ican Spine Society, which include a clinical diagnosisand imaging confirmation [51]. It should be noted, how-ever, that there is no universally agreed-on definition forLSS [1].

Conclusions

The findings of this review should be interpreted withcaution, because there are both limitations and gaps inthe related scientific literature that should be taken into ac-count. Also, all study populations were surgical cases andfindings may not apply to nonsurgical cases, which maybe less severe. Nonetheless, this review suggests that de-pression is likely a prognostic factor for the outcomes ofLSS-related symptom severity and disability in patients re-ceiving surgery for LSS and should be considered in thecare of such patients. The prognostic value of depressionon the outcomes of pain and walking capacity is less clear.

Appendix

Supplementary data

Supplementary data related to this article can be found athttp://dx.doi.org/10.1016/j.spinee.2013.09.052.

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depression as a prognostic factor of lumbar spinal stenosis: a systematic review

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