Reasons for failure to diagnose:
(1) failure to consider the diagnosis
(2) infection overshadowed by other opportunistic infections
(3) assumed to be some other infection (toxoplasmosis if encephalitis; PCP if pneumonia; bacteria, fungus or virus if keratitis)
(4) misidentified organism on smear or biopsy as a fungus or macrophage
(5) misreading of a Gram stain as positive for bacteria
When to consider acanthamebiasis:
(1) immunosuppressed or immunocompromised patient
(2) presence of granulomas or aggregates of macrophages (granulomas may be poorly formed if severely immunocompromised)
(3) presence of angiitis
(4) negative bacterial and fungal cultures
(5) failure to respond to antibiotics or antifungal agents
(6) presence of 2 or more: encephalitis, rhinitis, skin nodules/ulcers
