A mycotic infection of man or animals caused by a number of hyaline (non-dematiaceous) hyphomycetes where the tissue morphology of the causative organism is mycelial. This separates it from phaeohyphomycosis where the causative agents are brown-pigmented fungi. Hyalohyphomycosis is a general term used to group together infections caused by unusual hyaline fungal pathogens that are not agents of otherwise-named infections; such as Aspergillosis. Etiological agents include species of Penicillium, Paecilomyces, Acremonium, Beauveria, Fusarium and Scopulariopsis.
The clinical manifestations of hyalohyphomycosis are many ranging from harmless saprophytic colonization to acute invasive disease. Ideally, individual disease states involving invasive fungal infection by a hyaline hyphomycete should be designated by specific description of the pathology and the causative fungal genus or species (where known); for example "pathology A" caused by "fungus X".
Predisposing factors include prolonged neutropenia, especially in leukemia patients or in bone marrow transplant recipients, corticosteroid therapy, cytotoxic chemotherapy and to a lesser extent patients with AIDS. The typical patient is granulocytopenic and receiving broad-spectrum antibiotics for unexplained fever.
1. Clinical material: Skin and nail scrapings; urine, 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 and nail scrapings, sputum, 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 PAS digest, Grocott's methenamine silver (GMS) or Gram stains. Note hyphal elements are often difficult to detect in H&E stained sections.
Interpretation: The presence of hyaline, branching septate hyphae, similar to Aspergillus 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.
3. Culture: Clinical specimens should be inoculated onto primary isolation media, like Sabouraud's dextrose agar.
Culture of Chrysosporium [left] and Fusarium [right] showing typical colony colour for a hyaline hyphomycete ie any colour except brown, olivaceous black or black.
Interpretation: The hyaline 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 hyalohyphomycosis.
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.
Acremonium sp., Beauveria sp., Fusarium sp., Paecilomyces sp., Penicillium sp., Scopulariopsis sp.
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