Chromoblastomycosis (chromomycosis) is a subcutaneous mycotic infection that is usually caused by traumatic inoculation of any of the recognized fungal agents, which reside in soil and vegetation. All are dematiaceous fungi, having melanized cell walls: P. verrucosa, F. pedrosoi, Fonsecaea compacta, Rhinocladiella aquaspersa, and Cladophialophora carrionii. The infection is chronic and characterized by the slow development of progressive granulomatous lesions that in time induce hyperplasia of the epidermal tissue.

Morphology and Identification

The dematiaceous fungi are similar in their pigmentation, antigenic structure, morphology, and physiologic properties. The colonies are compact, deep brown to black, and develop a velvety, often wrinkled surface. The agents of chromoblastomycosis are identified by their modes of conidiation. In tissue they appear the same, producing spherical brown cells (4–12 µm in diameter) termed muriform or sclerotic bodies that divide by transverse septation. Septation in different planes with delayed separation may give rise to a cluster of four to eight cells (Figure 1). Cells within superficial crusts or exudates may germinate into septate, branching hyphae.

Fig1. Chromoblastomycosis. The diagnostic brownish, melanized sclerotic cells (4–12 µm diameter) are evident in this H&E-stained cutaneous biopsy. 400×.

Cultures of these dematiaceous molds can be distinguished as follows:

A. P. verrucosa

The conidia are produced from flask-shaped phialides with cup-shaped collarettes. Mature, spherical to oval conidia are extruded from the phialide and usually accumulate around it (Figure 2A).

B. F. pedrosoi

The Fonsecaea genus is polymorphic. Isolates may exhibit (1) phialides; (2) chains of blastoconidia, similar to Cladosporium species; or (3) sympodial, rhinocladiella-type conidiation. Most strains of F. pedrosoi form short branch ing chains of blastoconidia as well as sympodial conidia (see Figure 2B).

C. F. compacta

The blastoconidia produced by F. compacta are almost spherical, with a broad base connecting the conidia. These structures are smaller and more compact than those of F. pedrosoi.

 D. R. aquaspersa

This species produces lateral or terminal conidia from a lengthening conidiogenous cell—a sympodial process. The conidia are elliptical to clavate.

E. Cladophialophora (Cladosporium) carrionii

Species of Cladophialophora and Cladosporium produce branching chains of conidia by distal (acropetalous) budding. The terminal conidium of a chain gives rise to the next conidium by a budding process. Species are identified based on differences in the length of the chains and the shape and size of the conidia. C. carrionii produces elongated conidiophores with long, branching chains of oval conidia.

Fig2. Identifying conidia produced in culture by the two most common agents of chromoblastomycosis. A: P. verrucosa produces conidia from vase-shaped phialides with collarettes. 1000×. B: F. pedrosoi usually displays short branching chains of blastoconidia, as well as other types of conidiogenesis. 1000×.

Pathogenesis and Clinical Findings

The fungi are introduced into the skin by trauma, often of the exposed legs or feet. Over months to years, the primary lesion becomes verrucous and wart-like with extension along the draining lymphatics. Cauliflower-like nodules with crusting abscesses eventually cover the area. Small ulcerations or “black dots” of hemopurulent material are present on the warty surface. Rarely, elephantiasis may result from secondary infection, obstruction, and fibrosis of lymph channels. Dissemination to other parts of the body is very rare, though satellite lesions can occur due either to local lymphatic spread or to autoinoculation. Histologically, the lesions are granulomatous, and the dark sclerotic bodies may be seen within leukocytes or giant cells.

Diagnostic Laboratory Tests

Specimens of scrapings or biopsies from lesions are examined microscopically in KOH for dark, spherical cells. Detection of the sclerotic bodies is diagnostic of chromoblastomycosis regardless of the etiologic agent. Tissue sections reveal granulomas and extensive hyperplasia of the dermal tissue. Specimens should be cultured on IMA or SDA with antibiotics. The dematiaceous species is identified by its characteristic conidial structures, as described above. There are many simi lar saprophytic dematiaceous molds, but they differ from the pathogenic species in being unable to grow at 37°C and being able to digest gelatin.

Treatment

 Surgical excision with wide margins is the therapy of choice for small lesions. Chemotherapy with flucytosine or itraconazole may be efficacious for larger lesions. The application of local heat is also beneficial. Relapse is common.

Epidemiology

Chromoblastomycosis occurs mainly in the tropics. The fungi are saprophytic in nature, probably occurring on vegetation and in soil. The disease occurs chiefly on the legs of barefoot agrarian workers following traumatic introduction of the fungus. Chromoblastomycosis is not communicable. Wearing shoes and protecting the legs probably would pre vent infection.

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