subcutaneous mycoses

SUBCUTANEOUS MYCOSES

• Mycetoma• Phaeohyphomycosis• Chromoblastomycosis • Sporotrichosis• Lobomycosis• Rhinosporidiosis

What is Mycetoma?

• Mycetoma is a chronic granulomatous, progressive inflammatory disease that involves the subcutaneous tissue after a traumatic inoculation of the causative organism

• It may be caused by true fungi (eumycetes) or by higher bacteria (actinomycetes) and therefore it is classified into eumycetoma and actinomycetoma respectively.

This infection results in a granulomatous inflammatory response in the deep dermis and subcutaneous tissue, which can extend to the underlying bone

Mycetoma is characterized by the formation of grains containing aggregates of the causative organisms that may be discharged onto the skin surface through multiple sinuses

The disease was originally reported from Madurai, it is therefore commonly known as Maduramycosis or Madura foot

It is seen mainly in tropics, though occasional cases have been reported from the temperate countries

Causative agents of eumycetoma

Madurella mycetomatisMadurella griseaExophiala jeanselmeiAcremonium sppAspergillus sppFusarium sppScedosporium (Pseudallescheria)

Pathogenesis

The causative agent is believed to enter through minor trauma

The disease usually begins as a small subcutaneous swelling of the foot, which enlarges, burrowing into the deeper tissues and tracking to the surface as multiple sinuses discharging viscid, seropurulent fluid containing granules

The lesions are pain less

It may spread to involve deep structures resulting in destruction of bone, deformity and loss of function with serious social and economic implications.

Mycetoma

Lab diagnosis

Demonstration of granules in the infected tissue

The colour and consistency of the granules vary with the different agents

In actinomycotic mycetoma, the grains are composed of very thin filaments, while in mycotic lesions, they are broader and often show septae and chlamydospores

Growth of organisms in culture and physiological and serological tests also help in establishing the diagnosis

Treatment

• Surgery

• Antifungal therapyAmphotericin B

Miconazole Ketoconazole Itraconazole

FlucytosineTopical nystatin Topical potassium iodide(choice of treatment varies according to the

infecting fungus)

Sporotrichosis

This is a chronic infection involving cutaneous, subcutaneous and lymphatic tissue

It is frequently encountered in gardeners, forest workers and manual labourers

Causative agent: The thermally dimorphic fungus Sporothrix schenckii

The fungus is found in soil, decaying woods, thorns and on infected animals including rats, cats, dogs and horses

Pathogenesis and clinical presentation

Spore is the infective stage of the fungus

It causes infection primarily on the hand or the forearm through direct contact of the skin by spores

Typically, infection is introduced in skin through a penetration of thorn

At the site of thorn injury, it causes a local pustule or ulcer with the nodules along the draining lymphatics

Frequently , the regional lymph nodes draining the ulcer enlarge, suppurate and ulcerate

The primary lesion may remain localized or in the immunocompromised individuals may disseminate to involve the bones, joints, lungs and rarely the central -nervous system

Laboratory diagnosis

Specimens

The samples to be collected include aspiration fluid, pus, biopsy material, skin scrapings and swabs

Microscopy

KOH mount of specimen or histopathological examination of tissue sections stained by methanamine silver stain

The characteristic feature is the asteroid body; a rounded or oval, basophilic, yeast-like body 3-5 um in diameter, with rays of an eosinophilic substance radiating from the yeast cell

Culture

The fungus may not be demonstrable in pus or tissue.

Hence, culture is done on media incubated at 250C and 370C

440

441

Serology

Serological tests are especially helpful in the diagnosis of extracutaneous or systemic infection

A slide latex agglutination test, using peptido-L-rhamno- D-mannan as antigen is a reliable, sensitive and specific test

Treatment

For cutaneous infection, potassium iodide given topically or orally

For lymphocutaneous infection, itraconazole is effective

For disseminated infection, amphotericin B is the drug of choice

Rhinosporidiosis

This is a chronic granulomatous disease characterised by the development of friable polyps, usually confined to the nose, mouth or eye but rarely seen on the genitalia or other mucous membranes

Distribution

Although the disesase was first identified in Argentina, most cases come from India and Srilanka

Causative agent: Rhinosporidium seeberi

R. seeberi cannot be cultured in cell-free artifical media

Aimal inoculation is also not successful

Pathogenesis and clinical features

The mode of infection of this fungus is not known

However, it is suggested that it is transmitted in dust and water

Fish is believed to be the natural host of this fungus

Infection is seen most commonly in persons taking bath in stagnant pools and in individuals who dive in streams to collect sand from river beds

The disease is characterized by the development of large friable ployps or wart-like lesion in the nose, conjunctiva or eye

The lesions can also be seen in buccal cavity, skin or genitalia

Laboratory diagnosis

Depends on demonstration of sporangia of R. seeberi in tissue sections stained with H & E or other special stains such as GMS stain and PAS stain

The sporangia measure 10-200 µm in diameter and contain thousands of endospores

H&E stain

Endospores and sporangia of Rhinosporidium seeberi

Treatment

Treatment of the condition is carried out by surgery or cauterization

Chemotherapy with dapsone is also useful