Subcutaneous phaeohyphomycosis caused by a black pigmented mould (Rhytidhysteron species) in rural north-western New South Wales, Australia

Abstract

Invasive fungal infections are becoming increasingly more prevalent in clinical practice. This corresponds with more patients living with immunosuppression and improved techniques to identify fungal infections. Subcutaneous fungal masses can often masquerade and imitate common dermatological lesions such as cysts. Querying a fungal aetiology of a mass is important, as fungal elements can be missed on histological examination, and special stains may be needed to identify spores and hyphae to make the diagnosis. Skin trauma with inoculation of fungal elements contained in soil and vegetable matter is the most common source of subcutaneous fungal masses. While traditionally considered a disease of the tropics, subcutaneous fungal masses can present worldwide in both immunosuppressed and immunocompetent patients.<br/><br/>This case study describes a subcutaneous knee mass in a 53-year-old immunosuppressed farmer in Australia. A subcutaneous phaeohyphomycosis was diagnosed with a black pigmented mould, <i>Rhytidhysteron</i> species. A latent period of 12 years was observed between traumatic inoculation with farm soil and wheat dust in north-western New South Wales and development of the knee mass.<i>Rhytidhysteron</i> is considered a disease of the tropics, most commonly reported in India. This case, to the author's knowledge, is the first case report of pathogenic <i>Rhytidhysteron</i> from Australia. Surgery and antifungal therapy are recommended to treat <i>Rhytidhysteron</i> infection. This patient's recommended antifungal treatment was shortened due to severe hepatic disease.<br/><br/>The clinical course was complicated by three localised recurrences in the patient's knee over 14 months. At the time of the third localised recurrence, this patient could tolerate posaconazole therapy for a month only. Surgical excision using general anaesthesia, use of diathermy for excision and wound lavage with iodine, hydrogen peroxide and saline has coincided in remission of clinical disease for 3 years at the time of writing.