Cytohistomorphology of subcutaneous phaeohypomycosis

Abstract

Phaeohypomycosis is a clinical syndrome caused by melanised or dematiaceous fungi characterized by the presence of brown mycelial structures in tissue section. These fungi are associated with a repertoire of the clinical manifestations that includes superficial and deep local infection to disseminated infection. Herein, we describe the clinical and fine-needle aspiration cytology and histopathologic features of a case of subcutaneous phaeohypomycosis.

Introduction

Phaeohypomycosis is a type of mycosis caused by dematiaceous fungi. These are melanin pigment producing fungi found in soil, wood, living and dead plant material. In the past two decades, these fungi have been reported as important pathogen distributed world-wide causing a spectrum of clinical manifestations such as allergic fungal sinusitis, onychomycosis, subcutaneous nodule, keratitis, bone and joint infection, peritonitis, pneumonia, cerebral abscesses and disseminated infection.[1,2,3,4,5] Although, there are case reports ascribing the histopathological features of subcutaneous phaeohypomycosis in 14 cases, the description about the aspiration cytomorphology is limited to only 3 cases.[2,3,4,5,6,7,8] Herein, we describe the clinical presentation, aspiration cytology and histomorphologic features of a case of subcutaneous phaeohypomycosis.

Case Report

A 40-year-old lady presented with a soft, nodular, mobile swelling of size 3.0 cm × 2.0 cm over the right forearm near the wrist joint; radiograph showed a soft-tissue swelling without bone involvement. Clinically, suspected to be ganglion with the differential diagnosis of soft-tissue tumor [Figure 1a]. fine-needle aspiration (FNA) yielded thick mucoid material. Leishman stained cytosmears showed numerous neutrophils, foamy macrophages, macrophages containing coarse dark granular pigments within the cytoplasm along with many degenerated cells, lymphocytes and occasional multinucleated giant cells [Figure 1b]. On questioning the patient gave a history of injury with wooden splinter. Considering the clinical and cytomorpholgic features, a diagnosis of acute on the chronic inflammation with a possibility of fungal infection was offered and advised excision biopsy.

Figure 1.

(a) Nodular swelling over the right forearm, (b) Cytosmear showing neutrophils, lymphocytes, foamy macrophages, macrophages containing dark pigment inside cytoplasm (Leishman, ×1000), (c) Microsection showing brown hyphae, eosinophilic Splendore-Hoeppli material at the periphery (H and E, ×400), (d) Microsection showing periodic acid-Schiff (PAS) positive magenta hyphae (PAS, ×400), (e) Microsection showing fungal colonies, chronic inflammatory cell infiltration and multinucleated giant cells (PAS, ×400), (f) Cytosmears showing dark brown pigment and unstained hyphae like structures (Pap, ×400)

Gross examination of the excised specimen showed a grey white ovoid tissue measuring 3.0 cm × 2.0 cm, cut section showed solid grey yellow and grey white area with focal black granular areas. Hematoxylin and eosin (H and E) stained microsections showed fungal colonies comprising of closely packed brown colored septate hyphae with acute angle branching and of narrow width along with eosinophilic Splenore-Hoepplie material at the periphery [Figure 1c]. Periodic acid-Schiff (PAS) stain revealed positive magenta colored hyphae [Figure 1d]. The surrounding fibrofatty tissue showed dense infiltrate of neutrophils, lymphocytes, eosinophils, foamy macrophages, macrophages containing coarse dark brown black colored pigments within the cytoplasm along with many multinucleated giant cells around the fungal colonies [Figure 1e].

No fungal hyphae were seen inside the giant cells. However, retrospective review of the routine cytosmears revealed focal dark brown black colored pigment with unstained hyphae like structures at the periphery, which was missed in the initial examination [Figure 1f]. The case was finally diagnosed as subcutaneous phaeohypomycosis. Fungal culture was not done in this case.

Discussion

Clinical syndrome caused by melanised or dematiaceous fungi are differentiated into three types based on the histologic findings i.e., eumycetoma, chromoblastomycosis and phaeohypomycosis. In histology sections, eumycetoma shows the presence of grains which are closely packed fungal hyphae; whereas, chromoblastomycosis shows sclerotic bodies consisting of thick walled muriform cells.[3] Phaeohypomycosis is characterized by the presence of dark brown mycelial structures in the involved tissue, which distinguishes it from the other clinical categories of disease caused by brown pigmented fungi. The dark brown color is due to production of melanin pigment in the fungal cell wall, which protects the organism by its scavenging action over free radicals and hypochlorites produced by host phagocytic cells.[5] Subcutaneous phaeohypomycosis usually occurs by traumatic implantation of fungal elements from contaminated soil, thorns or wood splinter. The disease usually occurs in immunocompromised patients or patients receiving immunosuppressive drugs like renal transplant patients.[6] There are reports on FNA cytology findings of subcutaneous phaeohypomycosis ascribing mostly features of inflammatory lesion comprising of acute and chronic inflammatory cells including multinucleated giant cells and epithelioid histiocytes in the FNA cytosmears along with the presence of brown pigmented hyphae in the form of budding yeast, pseudohyphae or septate hyphae with acute angle branching.[7,8] The exact diagnosis is based on careful pathologic examination of tissue sections with routine.

H and E stain and special stain like Gomori's methenamine silver stain or PAS stain with species identification by fungal culture. In the present case, FNA findings were suspicious of fungal lesion, which was subsequently confirmed by histopathologic examination of the tissue section along with special staining such as PAS. Retrospective review of the FNA cytosmears could reveal the presence of focal dark brown black pigment with unstained hyphae like structures at the periphery, which was missed in the initial examination. Hence, while evaluating the soft-tissue lesions in the extremities by FNA, possibility of such disease should also be considered. Meticulous examination of the routinely stained cytosmears also can give a clue to arrive at such diagnosis.