Infectious Disease and Microbiology – Chromoblastomycosis Agents

Overview

Chromoblastomycosis, also called chromomycosis or dermatitis verrucosa, is a chronic fungal infection of the skin and subcutaneous tissues caused by several dematiaceous (darkly pigmented) fungi. Infection typically follows traumatic implantation of the fungus into the skin and develops slowly over months to years.

The disease classically produces chronic verrucous or wart-like lesions of the lower extremities, particularly in barefoot agricultural workers living in tropical and subtropical regions.

Causative Species

Several fungi can cause chromoblastomycosis, including:

• Cladophialophora carrionii (formerly Cladosporium carrionii)

• Fonsecaea compacta

• Fonsecaea pedrosoi — the most common cause

• Phialophora verrucosa

• Rhinocladiella aquaspersa

These organisms are environmental fungi associated particularly with soil, vegetation, and decaying plant material.

Microbiologic Characteristics

The causative organisms are dematiaceous filamentous fungi, meaning that their cell walls contain melanin and therefore appear brown or darkly pigmented.

They characteristically form:

• Septate hyphae in culture

• Pigmented fungal elements in infected tissue

• Sclerotic bodies within tissue

The presence of sclerotic bodies is one of the most important diagnostic features of chromoblastomycosis.

Sclerotic Bodies

In tissue, the fungi transform into characteristic thick-walled, brown, rounded structures known as:

Sclerotic bodies

They are also called:

• Medlar bodies

• Muriform bodies

• Copper-penny bodies

They may divide along multiple planes, producing a characteristic appearance resembling copper pennies.

Sclerotic bodies in a chronic verrucous skin lesion are highly characteristic of chromoblastomycosis.

Incubation Period

The exact incubation period is uncertain because the infection progresses very slowly.

It is probably at least several months, and clinically apparent disease may develop long after the initial traumatic inoculation.

Epidemiology

Chromoblastomycosis occurs worldwide but is most prevalent in tropical and subtropical regions, particularly in developing countries.

It is associated strongly with:

• Rural residence

• Agricultural work

• Walking barefoot

• Frequent contact with soil and vegetation

• Minor penetrating injuries from thorns, wood, or plant material

The lower extremities are affected most often because they are particularly vulnerable to traumatic inoculation.

Pathogenesis

Infection usually begins when contaminated plant material or soil causes a small penetrating injury.

The fungus is introduced directly into:

Skin → subcutaneous tissue

The organism then produces a slowly progressive local inflammatory response.

Unlike many invasive fungal infections, chromoblastomycosis commonly occurs in otherwise immunocompetent individuals because infection results primarily from direct traumatic implantation rather than systemic acquisition.

Clinical Manifestations

Chromoblastomycosis is typically a chronic, slowly progressive cutaneous and subcutaneous infection.

The initial lesion may begin as a small papule or nodule at the site of traumatic inoculation.

Over time, it can enlarge and develop into:

• Verrucous plaques

• Warty nodules

• Papillomatous lesions

• Tumor-like masses

• Crusted plaques

Lesions may resemble large warts or cauliflower-like growths.

Typical Location

The most characteristic location is the:

Lower extremity

Feet and legs are especially commonly affected because of exposure to contaminated soil and vegetation.

Other body regions may occasionally become involved following traumatic implantation.

Chronic Disease

Progression is generally slow, often occurring over years.

As lesions enlarge, patients may develop:

• Secondary bacterial infection

• Ulceration

• Fibrosis

• Lymphatic obstruction

• Lymphedema

• Functional impairment

Extensive disease can become difficult to eradicate.

Dissemination

Chromoblastomycosis generally remains localized to the skin and subcutaneous tissues.

Rarely, deeper extension or dissemination can involve:

• Muscle

• Central nervous system

• Lungs

Such invasive disease is unusual.

Diagnosis

Diagnosis depends on demonstrating the characteristic fungal structures in affected tissue and identifying the causative organism by culture.

Histopathology

The classic diagnostic finding is:

Sclerotic bodies

These are brown, thick-walled fungal structures present within infected tissue.

Their appearance is sufficiently characteristic that identifying them in the appropriate clinical setting strongly supports chromoblastomycosis.

Culture

Fungal culture is used to determine the specific causative organism.

Identification depends on:

• Colony morphology

• Pigmentation

• Microscopic morphology

• Characteristic sporulation patterns

Culture is particularly useful because several different dematiaceous fungi can produce the same clinical syndrome.

Differential Diagnosis

Chronic verrucous lesions can resemble several infectious and noninfectious conditions, including:

• Sporotrichosis

• Mycetoma

• Cutaneous tuberculosis

• Leprosy

• Cutaneous leishmaniasis

• Phaeohyphomycosis

• Verrucous bacterial infections

• Squamous cell carcinoma

Finding sclerotic bodies helps distinguish chromoblastomycosis from other implantation mycoses.

Treatment

Treatment can be difficult, particularly when lesions are large or longstanding. There is no single universally effective regimen.

Management depends largely on lesion size, location, and extent.

Small Lesions

Small, localized lesions may be treated with:

Surgical excision

or

Cryotherapy

Complete removal is most successful when disease is detected early and remains well localized.

Itraconazole

Itraconazole is an important systemic treatment option.

Treatment usually needs to be prolonged:

At least 6 months, and often considerably longer depending on clinical response.

Itraconazole may be combined with:

• Cryotherapy

• Surgical excision

• Other local destructive techniques

Combination therapy can be particularly useful for larger or more persistent lesions.

Terbinafine

Terbinafine is another important systemic antifungal option and may be used alone or as part of combination management.

Extensive or Refractory Disease

For extensive disease, historical treatment approaches have included:

Flucytosine + amphotericin B

More recently, broad-spectrum triazole antifungals may have activity against some causative organisms.

Treatment should ideally be guided by the specific organism, disease severity, and clinical response.

Prevention

Because infection usually follows traumatic implantation, prevention focuses on protecting the skin from contaminated soil and vegetation.

Protective measures include:

• Wearing shoes or boots

• Wearing long trousers and protective clothing

• Wearing gloves during agricultural work

• Promptly cleaning penetrating skin injuries

These precautions reduce exposure to thorns, splinters, and other materials capable of introducing the fungus into subcutaneous tissues.

High-Yield Clinical Pattern

Barefoot agricultural worker in a tropical region

• ●

History of traumatic inoculation

• ●

Slowly progressive verrucous or cauliflower-like lesion on the leg

• ●

Brown sclerotic bodies on histology

→ Think chromoblastomycosis

Key Diagnostic Distinction

Chromoblastomycosis

→ Sclerotic (Medlar/copper-penny) bodies

Phaeohyphomycosis

→ Pigmented hyphae or yeast-like fungal elements in tissue, without characteristic sclerotic bodies

Mycetoma

→ Tumefaction + draining sinus tracts + grains

This distinction is particularly useful in microbiology and infectious disease examinations.

Exam Essentials

Disease: Chromoblastomycosis

Other names: Chromomycosis, dermatitis verrucosa

Organisms: Dematiaceous fungi

Most common species: Fonsecaea pedrosoi

Transmission: Traumatic implantation from soil or vegetation

Typical patient: Rural agricultural worker in a tropical/subtropical region

Typical site: Lower extremities

Typical lesion: Chronic verrucous/warty plaque or nodule

Characteristic tissue finding: Sclerotic bodies

Other names for sclerotic bodies: Medlar bodies, muriform bodies, copper-penny bodies

Diagnosis: Histopathology + fungal culture

Localized treatment: Excision or cryotherapy

Systemic treatment: Prolonged itraconazole or terbinafine

Prevention: Protective shoes and clothing

Key clinical pearl: The combination of a chronic verrucous lower-extremity lesion after traumatic soil or plant exposure and brown copper-penny–like sclerotic bodies in tissue is the classic presentation of chromoblastomycosis.