Subcutaneous pheohyphomycosis presenting as a innocuous pustule.

Pheohyphomycosis is a rare heterogeneous group of mycotic infections caused by dematiaceous (phaeoid) fungi affecting the skin, subcutaneous tissue, and central nervous system. Herein, we report a case of 29-year-old man with innocuous pustule over the right index finger. Examination revealed a subcutaneous swelling with pustules over the surface. Biopsy revealed phaeoid fungi, and diagnosis of subcutaneous pheohyphomycosis was made.

What was known?

Subcutaneous pheohyphomycosis is a rare type of fungal infection affecting the skin and subcutaneous tissue commonly.

Introduction

Pheohyphomycosis is a rare infection caused by a wide range of brown-pigmented (phaeoid) or dematiaceous fungi including Exophiala Jeanselmei, Exophiala Dermatitidis, Bipolaris, Alternaria species. It presents as a localized subcutaneous or deep-seated infection, usually a cyst or abscess. Though this condition is relatively commonly reported from Southern India, not a single report of subcutaneous pheohyphomycosis has been reported from this part of Karnataka.[1]

Case Report

A 29-year-old flour mill worker presented with swelling over the right index finger since 6 months. History of recurrent pustules with pain and difficulty in movement was present. No history of trauma was present. He was treated for rhinoscleroma 5 years back and was on intermittent self-medicated steroid (Tab prednisolone 5 mg/day). On examination, diffuse swelling was seen over the right index finger with innocuous pustules over the surface. No scarring was seen. Swelling was cystic in consistency with no discharging granules [Figure 1]. Regional lymph nodes were normal. ENT examination revealed a fibrotic nodule in the right nasal cavity with central perforation of septum with nasopharyngeal cicatrisation. Provisional diagnosis of recurrent furunculosis and subcutaneous fungal infection was made. Routine investigation like hemogram, blood sugar, liver and renal function tests were within normal limits. Chest x-ray was normal. ECG showed left ventricular hypertrophy. KOH was negative. Fungal culture of the aspirate showed no growth. Histopathology revealed multiple foreign body giant cell granuloma composed of histiocytes, plasma cells, Langhan's and foreign body giant cells [Figure 2]. The giant cells contain septate blackish-brown fungi along with yeast forms [Figure 3]. On PAS stain, septate brown fungi along with yeast forms were present [Figure 4]. Repeated culture did not reveal any growth. Therefore, a diagnosis of subcutaneous pheohyphomycosis was made, and patient was put on monthly pulse of itraconazole for 1 week and fluconazole for 3 weeks for a period of 3 months. There was marked improvement in lesions after 3 months of therapy [Figure 5].

Figure 1

Swelling over the right index finger with pustules over the surface

Figure 2

Foreign body giant cell granuloma composed of histiocytes, plasma cells, lymphocytes, Langhan's and foreign body giant cells (H and E, ×40)

Figure 3

Fungal elements with melanin in the dermis

Figure 4

On PAS stain, septate brown fungi along with yeast forms were present (ȕ100)

Figure 5

Lesion healed with scar

Discussion

One of the primary causes for an increase in fungal infection over the past several decades is believed to be the expanding population of immunocompromised individuals. One such group of opportunistic fungi is the (phaeoid) or dematiaceous fungi characterized by a single shared characteristic of possessing a darkly pigmented appearance.[23]

The term pheohyphomycosis[4] was coined by Ajello and collegues in 1974 to describe superficical, cutaneous and subcutaneous, and systemic infections, in which the etiological agent develops in the host tissue in the form of dark-walled dematiaceous septate mycelial element. Later, it was modified to include infection caused by brownish hyphal elements, pseudohyphae, yeast, and combination of these, irrespective of the identity of the etiological phaeoid fungi.[4] The cause of pigmentation is due to a melanin produced via a pentaketide pathway.[5]

Clinically, there are various categories of pheohyphomycosis like superficial, cutaneous, subcutaneous, and systemic (disseminated). Black peidra and tinea nigra are examples of superficial infection. Cutaneous diseases cause lesions similar to dermatophytes.[6] Subcutaneous infection probably originates by implantation from an exogenous source and may present as tender nodules, which may develop abscess or cyst. But, in our case, the patient presented with a innocuous pustule making diagnosis of subcutaneous fungal infection difficult. The lesions are situated characteristically over the extremities like fingers, wrist, and knee. No regional lymph nodes are involved.[7] Exophiala Jeanselmei is the most common cause in temperate climate.[6] Disseminated pheohyphomycosis is largely a disease of immunocompromised individuals and results by spread of fungi from a previously infected site to distant sites like heart, brain, joints, kidney, and liver and is associated with high mortality. Bipolaris Spicifera is the most common of disseminated phaeohphomycosis.[3] Even in our patient, there were features of multisystem involvement, but as the organism was isolated only from skin, a diagnosis of subcutaneous pheohyphomycosis was made.

Histologically, lesions are characterized by circumscribed phaeohyphomycotic cyst situated in the lower dermis. Brown staining hyphae and yeast cells are seen in the wall on special staining such as gomori methenamine silver or masson trichrome. Similar finding were noted in our case with melanin in the dermis. This contrasts with chromoblastomycosis, in which fungi appear as single thick wall muriform cells (sclerotic bodies).[6]

Treatment of subcutaneous and disseminated pheohyphomycosis includes surgical excision and anti-fungal therapy. Itraconazole has the best record. Other anti-fungal like fluconazole, terbinafine, voriconazole, amphotericin B are used singly or in combination. Our patient responded very well to combination of itraconazole and fluconazole.[68] This case has been reported for its simple presentation and clinical rarity.

What is new?

Subcutaneous pheohyphomycosis presenting as a innocuous pustule is rare.