Case 178. Alternariosis (48 y-o F)
    Biopsy from an infiltrative and ulcerative, nodular skin lesion on the knee, lasting for 13 years    
Key words : Alternaria alternata, airborne fungi
Alternaria alternata is a plant pathogen, and is usually non-pathogenic to humans. Alternariosis may rarely be seen in both healthy and immunocompromised hosts.   Intradermal abscess is formed (HE). The surrounding dermis reveals chronic fibrosing inflammation. In this case, no granulomatous reaction is seen.
Immunostaining using a 1:500 diluted patient's own serum discloses a positively labeled round pathogen in the abscess cavity (indirect immunoperoxidase).