Chromoblastomycosis is a chronic granulomatous infection of the skin and subcutaneous tissue caused by several different dematiaceous fungi (brown pigment producing) resulting in the formation of slow-growing, warty plaques, cauliflower-like lesions which may ulcerate. The fungi produce thick-walled, single or multicelled clusters ( sclerotic or muriform bodies). The fungi are introduced into the body usually by trauma, and hence, the lesions are mostly found in exposed parts of the body. The disease runs a chronic course and most cases can be treated to the point of cure.
The disease can be caused by a large number of fungi. They are dematiaceous, i.e., producing brown pigment. The most common fungi are Cladosporium carrionii, Phialophora verrucosa, and Fonsecaea pedrosoi. Less common pathogens are Fonsacea compactum, Exophiala spinifera, Rhinocladiella aquaspersa, Exophiala jeanselmei, and Wangiella dermatitidis. The fungi have been isolated from wood and soil and enter the body following trauma. The condition is usually found in rural communities.
The disease is found throughout the world including Central, South and North America, Cuba, Jamaica, Martinique, India, South Africa, Madagascar, Australia, and northern Europe. It is much more common in the tropics and subtropics. It is more common in agricultural workers. Adult male agricultural workers are most often affected, but the condition also has been reported in children.
The fungi enter the skin following trauma, evoking a granulomatous response. The epidermis shows pseudoepitheliomatous hyperplasia. In the dermis, a granuloma composed of epithelioid cells and Langhans giant cells are seen. The fungal elements can be seen as sclerotic bodies which are brown septate cells. The sclerotic bodies (medlar bodies/ muriform bodies/copper pennies) are extruded transepidermally, and they are seen as black dots on the surface of the lesion. This is characteristic of chromoblastomycosis.
The histology is that of a foreign-body granuloma with isolated areas of microabscess formation. In the organized granuloma, mainly within giant cells, groups of fungal cells may be seen. They are chestnut or golden brown, and therefore can be easily distinguished in the infiltrate. The cells are characteristically divided into several planes of division by thick septa and are termed muriform or sclerotic cells. There is marked pseudoepitheliomatous hyperplasia of the epidermis, and in some areas, apparent transepidermal elimination of fungal cells, which can be found in the stratum corneum The tissue between the granulomatous nodules shows chronic fibrosis. When ulceration has occurred, there is usually a secondary bacterial infection.
Usually, the disease will remain localized with slow peripheral extension. There can be central scarring. The early lesion can occasionally be an ulcer. After months or many years, large hyperkeratotic masses are formed. They can be as large as 3 cm thick. Secondary ulceration can occur, however, the lesion is usually painless. Satellite lesions are produced by scratching. In some cases, there can be lymphatic spread resulting in the sporotrichoid pattern. Hematogenous dissemination is very rare, but brain abscesses have been described. The secondary infection eventually may lead to lymphatic stasis and production of elephantiasis. Some forms may develop psoriasiform lesions. Squamous cell carcinoma may develop in chronic cases.
Usually, following trauma, a small warty papule appears. It enlarges very slowly to form a thick, hypertrophic, verrucous plaque. The lesion is, by and large, asymptomatic, though some patients may complain of occasional itching. Black dots (sclerotic bodies) will be seen on the surface of the plaque. These are fungal bodies eliminated transepidermally. They are usually solitary, but a few small lesions may also be seen in the periphery. These peripheral lesions are more common when there is itching. In some lesions, the plaque is flat and expands slowly with central scarring. The lesion is usually painless but can be painful in the presence of secondary infection. There can be lymphatic spread to adjacent areas.
Scraping from the surface of the lesion will show sclerotic bodies. They are brownish septate cells seen singly or in clusters. The surface is scraped and 10% potassium hydroxide (KOH) is added to the scrapings which are then viewed under the microscope.
Histopathology will show pseudoepitheliomatous hyperplasia of the epidermis. The dermis shows granuloma composed of epithelioid cells and Langhans giant cells. There can be collections of eosinophils, lymphocytes, and plasma cells. Within the giant cells and also free in the tissue, dark brown thick walled ovoid or spheric spores (sclerotic bodies/medlar bodies/copper pennies) can be seen. In culture, the colonies of all species are dark grey-green to black and velvety or downy with a black reverse. Three forms of conidial production are observed, acropetal budding, production of phialides, and sympodial conidiation.
Single small lesions can be excised followed by antifungal therapy. If surgery is not feasible, oral antifungals alone can be given. The antifungal drugs of choice are, itraconazole 200-400 mg/day or terbinafine, 250-500 mg/day given for a period varying from 6 months to a year or more. Flucytosine alone or combined with amphotericin also may be effective. Oral supersaturated potassium iodide solution is another choice. Other approaches to treatment are cryotherapy or local application of heat.
In the differential diagnoses, other verrucous lesions like tuberculosis verrucosa cutis, verruca vulgaris, blastomycosis, leishmaniasis, syphilis, yaws verrucous hemangioma, hypertrophic lichen planus, and lupus vularis may be considered. In the sporotrichoid type in which linear lesions occur, sporotrichosis is a very close differential diagnosis. Presence of black dots on the surface which are due to the transepidermal elimination of fungal elements is the most important differentiating feature from other conditions. The black dots can be scraped preferentially from the surface and viewed under the microscope after adding 10% KOH.
The disease can be treated to the point of cure. Early intervention will yield better results with little morbidity. Long-standing cases which are over joints and with lymphatic involvement have relatively high morbidity. Disseminated disease with involvement of the central nervous system has the worst prognosis. Prolonged treatment with hepatotoxic drugs is another factor which has to be considered. Best results are seen in small lesions which are amenable to surgery and followed up with antifungal therapy.
Surgical treatment, though highly effective, may not be feasible due to lesions being present over joints. The duration of antifungal therapy is highly variable, and patient compliance can become a deciding factor.