Case 179. Protothecosis (66 y-o M)
    Biopsy from an irregular infiltrative nodule on the dorsum of the hand of a farmer who cultivates Japanese oranges    
Key words : Prototheca wickerhamii, protothecosis
Pustules and fistulas are formed in the infiltrative plaque. In the subcutaneous tissue of the upper arm, multiple metastatic nodules are formed.   Protothecosis is a rare infection by achlorophilic algae, resulting from traumatic innoculation. Epithelioid granulomas with central necrosis are formed in the dermis (HE).
Closer view of necrotizing epithelioid granuloma in the dermis, resembling granulomatous lesions of other causes (HE). Pathogens are difficult to see in H&E preparation in this case.   The sporangia containing endospores are positively stained with PAS sequence. Protothecal sporangia are much smaller than those of Coccidioides immitis.
Grocott's silver demonstrates morule-like internal septation. The microbes are seen among the necrotic material.   A wood splinter is noted in the dermis, adjacent to the granulomatous cutaneous lesion. Prototheca is widely seen in the tree, soil, gut of the fish, etc.
Reference case 179A
Another biopsied specimen of protothecosis of the facial skin in a 64 y-o diabetic female (HE). In this case, morule-like sporangia are observable among the inflammatory background. The disease is often encountered as opportunistic infection.
  Reference case 179A
Protothecal granuloma, accompanying PAS-positive pathogens phagocytized by multinucleated giant cells (PAS). The sporangia are seen as PAS-positive, thick-walled spherical bodies.
Reference case 179A
Cultured Prototheca wickerhamii showing a morule-like internal septation (Papanicolaou). Typical morphology of protothecal sporangia is presented. It can be cultured on Sabouraud's medium.