Published on March 9, 2014
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 mycetomatis Madurella grisea Exophiala jeanselmei Acremonium spp Aspergillus spp Fusarium spp Scedosporium (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.
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 therapy Amphotericin B Miconazole Ketoconazole Itraconazole Flucytosine Topical 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
Serology Serological tests are especially helpful in the diagnosis of extracutaneous or systemic infection A slide latex agglutination test, using peptido-L-rhamnoD-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
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