anomalous innervations by;chaman lal

ANOMALOUS INNERVATIONS

Chaman Lal Karotia (CK)B.S.PT(KU); MPPS(Pak);

PG (Clinical NeurophysiolgyTechnology),(AKUH);Member of AANEM; Member of ASET;

Aga Khan University Hospital , Karachi.

INNERVATIONS

What is anomaly?� a·nom·a·ly (-nm-l) n:Gk, anomalos, irregular

A deviation from what is regarded as normal or normor norm

Or Marked deviation from normal, especially as a result of congenital or hereditary defects. anomalous, adj

Anomalous Innervations By:CK 315-X-12

Why is Important to know?

� If these conditions remain unrecognized,they can be mistakenly interpreted asthey can be mistakenly interpreted aspathological conditions or technical faults.

15-X-12 4Anomalous Innervations By:CK

A-Upper limb anomalous innervations

� Martin – Gruber Anastomosis (Median to Ulnar anastomosis)

� All Ulnar- hand innervations� Ulnar to median anastomosis� Superficial Radial nerve innervations on

dorsum of the hand


B-Lower limb anomalous innervations

� Accessory Peroneal nerve� Tibial to Peroneal anastomosis� Tibial to Peroneal anastomosis


Martin- Gruber anastomosis� It is most common anomalous innervation in

upper limb.� Present in 15 – 30 % of patients.� It is manifested by cross over of median-to-

ulnar fibres.ulnar fibres.� Cross over commonly occurs in mid forearm

either from the main median trunk or fromone of its branches (most commonly anteriorinterossius nerve).

� It may present unilaterally or bilaterally.� It involves only motor fibres.15-X-12 7Anomalous Innervations By:CK

Pathway and Innervation!� After cross over in the mid forearm, median

fibres run with the distal ulnar nerve toinnervate via any of the following means:

1. Innervation to hypothenar muscles(abductordigiti minimi).

2. Innervation to FDI muscle.Innervation to the ulnar innervated thenar3. Innervation to the ulnar innervated thenarmuscles.

4. Combination of these.


When is it recognized ?

� During routine ulnar conduction studies.� During ulnar conduction studies when

recorded from FDI.recorded from FDI.� During routine median studies.� When co- existent CTS study is

performed.


Recording During Routine Ulnar Studies

� If anastomotic fibres innervate abductor digitiminimi, > 10 % drop in CMAP amplitude isnoted between wrist and below elbowstimulation sites.( Higher amplitudes are seenstimulation sites.( Higher amplitudes are seenwith distal stimulation).

� Median nerve stimulation should be performedat the wrist and at the antecubital fossa (AF)while recording the hypothenar muscles.


NCS recording from ADQ muscle


Cont’d…� The differential diagnosis of this pattern (i.e.,

higher amplitude distally than proximally) includesthe following:

� 1) Excessive stimulation of the ulnar nerve at thewrist resulting in co-stimulation of the mediannerve,2) Submaximal stimulation of the ulnar nerve at the� 2) Submaximal stimulation of the ulnar nerve at thebelow-elbow site,

� 3) Conduction block of the ulnar nerve between thewrist and below-elbow sites, or

� 4) An MGA with crossing fibers innervating thehypothenar muscles.


Cont’d…

� If no MGA is present, a small positivedeflection usually is recorded with both thewrist and antecubital fossa stimulation sites,reflecting a volume conducted potential frommedian muscles.

� If an MGA is present, a small positive� If an MGA is present, a small positivevolume-conducted potential will be presentwith median nerve stimulation at the wrist;however, median stimulation at theantecubital fossa will evoke a small CMAPover the abductor digiti minimi.


� The amplitude of the CMAP evoked bystimulating the median nerve at the ante-cubital fossa (recording the hypothenarmuscles) will approximately equal thedifference between the CMAP amplitudesevoked with ulnar nerve stimulation at the

Cont’d…

evoked with ulnar nerve stimulation at thewrist and below-elbow sites (recording thehypothenar muscles).

� If its not identified it may give a falseimpression of technical fault or conductionblock.


NCS recoding from ADQ


Cross over of median to ulnar fibres supplying FDI

� If anastomotic fibres innervate FDI, >10 % ofamplitude drop occurs between stimulation atthe wrist and below-elbow site. Higheramplitude being found by distal stimulation.amplitude being found by distal stimulation.

� It may give a false impression of technicalmistake or conduction block.

� Question:- When NCS from FDI is done?


How to confirm for MGA ?

� After ruling out the technical faults, mediannerve is stimulated at wrist and at anticubitalfossa while recording from FDI.

� Higher amplitude CMAP is recorded withproximal stimulation than with wristproximal stimulation than with wriststimulation in case of MGA.

� The difference between wrist and anticubitalfossa stimulations approximates the drop inamplitude between proximal and distalstimulation sites when stimulating ulnarnerve.


NCS recording from FDI muscle


Cross over of median-to-ulnar fibres innervating any of the ulnar innervated thenar muscles.

� Adductor pollicis and deep head of flexor pollicisbrevis are ulnar nerve innervated thenarmuscles.When these muscles are innervated by MGA,� When these muscles are innervated by MGA,median motor studies show a characteristicpattern of higher CMAP amplitudes withproximal median stimulation than distalstimulation.


NCS recording from APB muscle


How to confirm for MGA ?

� After ruling out the technical faults, ulnar nerve isstimulated at the wrist and below elbow siteswhile recording from thenar muscles.

� Normally it results in a CMAP (due to ulnar� Normally it results in a CMAP (due to ulnarinnervated muscles in thenar eminence) ofalmost same amplitude, with proximal as well asdistal stimulation.

� If an MGA is present, CMAP amplitude is lowerwith proximal stimulation.


MGA with co existent CTS

� As both of these conditions are common, so theymight be seen existing together.

� Co existence of both the conditions should besuspected when proximal median nervestimulation gives a more positive deflection atstimulation gives a more positive deflection atthe thenar eminence along with fast conductionvelocity.

� In some cases of severe CTS, proximal latencymay be shorter than the distal latency.


Needle EMG in case of MGS

� In this situation, unexpected results may be seencreating confusion in interpretation. Forexample,

� In cases of median nerve dysfunction at theIn cases of median nerve dysfunction at theanticubital site, EMG may show abnormalfindings in ulnar innervated muscles.

� In cases of ulnar neuropathy, some of the ulnarinnervated muscles may be spared on EMGexamination.


All Ulnar- hand innervations� Among them are cases of the all-ulnar

hand. In rare individuals, all or most of theintrinsic hand musculature is innervated bythe ulnar nerve. In these individuals, anthe ulnar nerve. In these individuals, anulnar nerve lesion at the elbow may causemuch more dysfunction in the hand thanone typically expects to see.


Anomalous innervation between Superficial Radial and the Dorsal Ulnar Cutaneous

sensory nerves� In the upper extremity, an anomalous

innervation between the superficial radial andthe dorsal ulnar cutaneous sensory nerves hasbeen described. Normally, sensation to thebeen described. Normally, sensation to thedorsum of the hand is mediated by bothnerves: the little and ring fingers and medialhand by the dorsal ulnar cutaneous nerve, andthe remainder by the superficial radial nerve. Inrare individuals, the superficial radial nerveinnervates the entire territory.


NCS recording in Sup.Radial v/s DUC

� During nerve conductions, this situation maypresent as an apparently absent responserecording the dorsal ulnar cutaneous sensorynerve.nerve.

� The anomaly can be demonstrated bystimulating the superficial radial nerve in thelateral forearm, with recording electrodesplaced over the dorsal ulnar cutaneous nerveterritory.


Accessory Peroneal Nerve (APN)� The most common anomalous innervation in

the lower extremity is the accessoryperoneal nerve (APN) in the lateral calf.

� Patients with an APN have an anomalousinnervation to the EDB; the medial portion ofinnervation to the EDB; the medial portion ofthe EDB is supplied by the deep peronealnerve as usual, but the lateral portion issupplied by an anomalous motor branchoriginating from the superficial peronealnerve, the APN.


Tibial to Peroneal anastomosis

� In addition, there are rare isolated casereports of tibial-to-peroneal and ulnar-to-median anastomosis. If an unusual ormedian anastomosis. If an unusual orunexpected nerve conduction pattern isseen, one should always consider not onlytechnical factors but also the possibility ofan anomalous innervation.


Question :- All of the following can cause a“positive dip” on routine NCS EXCEPT?

� A. Co-stimulation.� B. Improper recording electrode placement.� C. MGA.� D. MGA with CTS.� E. Submaximal stimulation.


Answer:- C

� Explanation:- When recording over thethenar eminence and stimulating themedian nerve at the elbow, a positive dipmedian nerve at the elbow, a positive dipis not usually seen unless there isconcomitant CTS slowing down the actionpotentials as they enter the hand.


Question:- In the MGA:

� A. Some muscles in the thenar eminencethat are typically innervated by the mediannerve are innervated by the ulnar nerve.

� B. The proximal median amplitude is always� B. The proximal median amplitude is alwayshigher than the distal median amplitude.

� C. A pseudo-conduction block of the ulnarnerve in the forearm may occur.


Cont’d. . .

� D. The sensory potential recording fromdigit two has contributions from themedian and ulnar nerves.

� E. Individuals who have this variant may� E. Individuals who have this variant mayhave relative protection from medianneuropathy at the wrist.


Answer:- C

� Explanation:- An MGA involving the ADQwould be expected to produce a drop inamplitude when comparing the distal siteamplitude when comparing the distal sitewith the proximal site. This will have anappearance of conduction block in theforearm and not across the elbow.


anomalous innervations by;chaman lal

News & Politics

ulnar nerve stimulation

median stimulation

ulnar fibres

fdi muscle15x

distal ulnar nerve toinnervate

ulnar innervated thenarmuscles

stimulation atthe wrist

peroneal anastomosis15x