Cutaneous Fungal Bipolaris Infection

Presentation

A healthy 55-year-old man suffered a superficial skin abrasion to the left medial ankle while working at a sewage treatment plant. The abrasion progressed to a shallow ulcer with surrounding erythema over the next 4 to 5 days. A worsening course over the following 3 weeks prompted referral to the authors’ facility for further evaluation. Initial examination revealed an exquisitely tender, shallow ulcer, measuring approximately 8 cm x 5 cm with a necrotic base and extensive surrounding erythema (Figure 1).

Diagnosis

Culture results from a wound biopsy revealed dematiaceous hyphomycete fungi, Bipolaris, as the primary infectious agents. Histologically, the wound biopsy demonstrated chronic superficial and deep perivascular dermatitis. Pathogens noted on smear cultures included minor amounts of Staphylococcus aureus, Pseudomonas aeruginosa, and Streptococcus agalactiae.

Discussion

Dematiaceous fungi are characterized by the presence of pale to dark brown melanin-like pigment in their cell walls.¹ Clinical infections caused by dematiaceous fungi are classified as chromomycoses, mycetomas, or phaeohyphomycoses.^1–3 First described in 1922, chromomycoses are chronic, localized, subcutaneous or cutaneous infections characterized by sclerotic bodies in tissue called muriform cells.^1–3 In contrast, mycetomas are chronic infections of the skin and subcutaneous tissue with the potential to invade adjacent bone. This condition is characterized by anatomic distortion, draining sinus tracts, and distinctive granules composed of fibrin-covered fungal hyphae.³ First described by Ajello et al.⁴ in 1974, phaeohyphomycosis are superficial, cutaneous, subcutaneous, corneal, or systemic infections characterized by dematiaceous mycelial elements, which include hyphae, pseudohyphae-like structures, and yeast-like cells in tissue with variable pigmentation of the fungus.^1–4
The dematiaceous fungi comprise a large and heterogeneous group of molds found in decaying vegetables, rotting wood, forest carpets, dust, and soil.^2,3 Infections are most common in warm, humid, tropical and subtropical climates.² The infections caused by dematiaceous fungi, or “black fungi,” include the Bipolaris species and other pathogens found in humans caused by the Alternaria species, Cladophialophora bantiana, Curvularia species, Exophiala species, Exserohilum species, Fonsecaea pedrosoi, Madurella species, Phialophora species, Scedosporium prolificans, Scytalidium dimidiatum, and Wangiella dermatitidis.^1,2 Different strains of Bipolaris that can act as human pathogens include Bipolaris australiensis, Bipolaris hawaiiensis (implicated in sinusitis and lung infections), Bipolaris maydis, Bipolaris melanidis, Bipolaris spicifera, and Bipolaris sorokiniana.⁵ Microscopically, the genera Bipolaris is characterized by oblong conidia (asexual spores) with slightly protruding hila that are truncated or squared-off at the base and are continuous with the conidial wall.^6,7 They produce conidiophores (asexual spore-producing and spore-bearing hyphae) that grow in a sympodial manner in which the conidiophore increases in length by forming a new growing point below each new terminal conidium.^6,7
Infections caused by Bipolaris are often misdiagnosed as Drechslera or Helminthosporium. Drechslera or Helminthosporium have similar dark cell wall stains but different microscopic morphologies. Drechslera and Helminthosporium have not, however, been documented to cause human disease.⁶Bipolaris spicifera accounts for most Bipolaris infections, including meningoencephalitis, pneumonia, peritonitis associated with peritoneal dialysis, sinusitis, keratitis, and disseminated disease.^1,6,7 There are increasing cases reported in immunocompromised individuals as a result of cancer-related immunosuppression, HIV, or solid organ transplant.² Bipolaris species are the most common causes of phaeomycotic sinusitis and often present in immunocompetent individuals with allergic rhinitis. In the latter case, allergic rhinitis can be a risk factor or a manifestation of Bipolaris infection.^5,6
Bipolaris species are rarely implicated in cutaneous infections. Robb et al.⁸ recently reported superficial cutaneous Bipolaris in 3 patients without predisposing medical conditions. Straka et al.³ reported a case of a nonhealing cutaneous ulcer due to Bipolaris species in a pancytopenic patient presenting with acute leukemia following traumatic injury. Inoculation of minor wounds with fungi from contaminated sources appears to be closely associated with wound exacerbation and infection.^2,3
Histopathologic examination and mycologic studies are essential to diagnose and demonstrate the combination of characteristics that are specific to Bipolaris. Microscopic examination will differentiate between the fungal species Bipolaris, Drechslera, and Exserohilum and identify characteristics of conidial shape, the presence or absence of a protruding hilum, the contour of the basal portion of the conidium and hilum, and the point where the germ tube originates from the basal cell.^5,6
In the immunocompromised patient, surgical excision is reported as the treatment of choice for localized cutaneous Bipolaris infection with or without adjunctive systemic antifungal chemotherapy.³ Previous reports have demonstrated successful use of itraconazole andamphotericin B as systemic antifungal chemotherapeutic agents.³ Voriconazole has been shown to be efficacious and has demonstrated good fungistatic and fungicidal activities against dematiaceous fungi by in-vitro analyses.⁹ The decision for prompt aggressive surgical intervention is based on the prevention oflocal expansion, cosmetic deformity, and possible dissemination.³ Disseminated disease should be treated with systemic antifungal chemotherapy.^3,5,6

Management

The patient was admitted to the hospital for wound care and diagnosis. Initial identification of dematiaceous hyphomycete and bacterial colonization prompted initial therapy with intravenous (IV) voriconazole and topical silvadene, which failed to improve the course. Bipolaris species were confirmed, and IV treatment was changed to itraconazole. Surgical intervention was contemplated, but wound improvement was observed over the following 7 days. Outpatient treatment with oral itraconazole was continued after discharge. Complete wound healing was noted at the 10-week follow-up (Figure 2).

Conclusion

Cutaneous Bipolaris infection is a rare cause of chronic, nonhealing ulcers. Chronic ulcers caused by Bipolaris have been reported in immunocompromised patients, including those with leukemia.³ The dematiaceous fungi, meaning “black fungi,” are so named due to the presence of dark melanin-like pigment in their cell walls.¹ Bipolaris species are often misdiagnosed as nonpathogenic Drechslera or Helminthosorium—careful microscopic identification can differentiate the categories. Traumatic inoculation associated with contamination from environmental sources is a common etiologic factor. Appropriate treatment consists of amphotericin B or itraconazole with surgical excision if necessary.