A mycotic infection of humans and lower animals caused by a number of dematiaceous (brown-pigmented) fungi where the tissue morphology of the causative organism is mycelial. This separates it from other clinical types of disease involving brown-pigmented fungi where the tissue morphology of the organism is a grain (mycotic mycetoma) or sclerotic body (chromoblastomycosis). The etiological agents include various dematiaceous hyphomycetes especially species of Exophiala, Phialophora, Wangiella, Bipolaris, Exserohilum, Cladophialophora , Phaeoannellomyces, Aureobasidium, Cladosporium, Curvularia and Alternaria. Ajello (1986) listed 71 species from 39 genera as causative agents of phaeohyphomycosis.
Clinical forms of phaeohyphomycosis range from localized superficial infections of the stratum corneum (tinea nigra) to subcutaneous cysts (phaeomycotic cyst) to invasion of the brain. Ideally, individual disease states involving an invasive fungal infection by a dematiaceous hyphomycete should be designated by a specific description of the pathology and the causative fungal genus or species (where known); for example "pathology A" caused by "fungus X".
1. Subcutaneous phaeohyphomycosis:
Subcutaneous infections occur worldwide, usually following the traumatic implantation of fungal elements from contaminated soil, thorns or wood splinters. Exophiala jeanselmei and Wangiella dermatitidisare the most common agents and cystic lesions occur most often in adults. Occasionally, overlying verrucous lesions are formed, especially in the immunosuppressed patient.
Subcutaneous phaeohyphomycosis caused by Exophiala jeanselmei.
Subcutaneous phaeohyphomycosis caused by Wangiella dermatitidis.
2. Paranasal sinus phaeohyphomycosis:
Sinusitis caused by dematiaceous fungi, especially species of Bipolaris, Exserohilum, Curvularia and Alternaria is increasingly being reported, especially in patients with a history of allergic rhinitis or immunosuppression.
3. Cerebral phaeohyphomycosis:
Cerebral phaeohyphomycosis is a rare infection, occurring mostly in immunosuppressed patients following the inhalation of conidia. However, cerebral infections caused by Cladophialophora bantianahave been reported in a number of patients without any obvious predisposing factors. This fungus is neurotropic and dissemination to sites other than the CNS is rare.
1. Clinical material: Skin scrapings and/or biopsy; sputum and bronchial washings; cerebrospinal fluid, pleural fluid and blood; tissue biopsies from various visceral organs and indwelling catheter tips.
2. Direct Microscopy: (a) Skin scrapings, sputum, bronchial washings and aspirates should be examined using 10% KOH and Parker ink or calcofluor white mounts; (b) Exudates and body fluids should be centrifuged and the sediment examined using either 10% KOH and Parker ink or calcofluor white mounts, (c) Tissue sections should be stained using H&E, PAS digest, and Grocott's methenamine silver (GMS).
Interpretation: The presence of brown pigmented, branching septate hyphae in any specimen, from a patient with supporting clinical symptoms should be considered significant. Biopsy and evidence of tissue invasion is of particular importance. Remember direct microscopy or histopathology does not offer a specific identification of the causative agent.
Note: direct microscopy of tissue is necessary to differentiate between chromoblastomycosis which is characterized by the presence in tissue of brown pigmented, planate-dividing, rounded sclerotic bodies and phaeohyphomycosis where the tissue morphology of the causative organism is mycelial.
3. Culture: Clinical specimens should be prepared as outlined in the chapter 2 and inoculated onto primary isolation media, like Sabouraud's dextrose agar.
Culture of Cladosporium [left] and Phialophora [right] showing typical brown, olivaceous black or black colony colour for a dematiaceous hyphomycete.
Interpretation: The dematiaceous hyphomycetes involved are well recognized as common environmental airborne contaminants, therefore a positive culture from a non-sterile specimen, such as sputum or skin, needs to be supported by direct microscopic evidence in order to be considered significant. A supporting clinical history in patients with appropriate predisposing conditions, is also helpful. Culture identification is the only reliable means of distinguishing these fungi.
4. Serology: There are currently no commercially available serological procedures for the diagnosis of any of the infections classified under the term phaeohyphomycosis.
5. Identification: Culture characteristics and microscopic morphology are important, especially conidial morphology, the arrangement of conidia on the conidiogenous cell and the morphology of the conidiogenous cell. Cellotape flag and/or slide culture preparations are recommended.
Alternaria sp., Aureobasidium pullulans, Bipolaris sp., Cladophialophora bantiana, Curvularia sp., Drechslera sp., Exophiala jeanselmei, Exophiala spinifera, Exophiala sp., Exserohilum sp., Phialophora verrucosa, Wangiella dermatitidis.
Ajello L and R.J. Hay. 1997. Medical Mycology Vol 4 Topley & Wilson's Microbiology and Infectious Infections. 9th Edition, Arnold London.
Ellis MB. 1971 and 1976. Dematiaceous Hyphomycetes and More Dematiaceous Hyphomycetes. International Mycological Institute.
Hoog de GS et al. 1977. The black yeasts and allied hyphomycetes. Studies in Mycology N0. 15 from Centraalbureau voor Schimmelcultures, Baarn, The Netherlands. CBS publications may be ordered from Tinke van den-Berg-Visser, Centraalbureau voor Schimmelcultures, PO Box 273, 3740 AG Baarn, The Netherlands FAX + 31 2154 16142.
Hoog de GS and J Guarro. 1994. Atlas of Clinical Fungi from Centraalbureau voor Schimmelcultures, Baarn, The Netherlands. CBS publications may be ordered from Tinke van den-Berg-Visser, Centraalbureau voor Schimmelcultures, PO Box 273, 3740 AG Baarn, The Netherlands FAX + 31 2154 16142.
Kwon-Chung KJ and JE Bennett 1992. Medical Mycology Lea & Febiger.
McGinnis MR. 1980. Laboratory handbook of medical mycology. Academic Press [this is out of print but a copy would be a valuable acquisition].
Richardson MD and DW Warnock. 1993. Fungal Infection: Diagnosis and Management. Blackwell Scientific Publications, London.
Rippon JW. 1988. Medical Mycology WB Saunders Co.
Warnock DW and MD Richardson. 1991. Fungal infection in the compromised patient. 2nd edition. John Wiley & Sons.