Prototheca osteomyelitis in a dog.

Canine systemic protothecosis is an uncommon disease caused by Prototheca spp., which are saprophytic algae occurring ubiquitously in nature. Infection occurs most commonly in immunocompromised animals. Most infected dogs have chronic large-bowel diarrhea, ocular lesions, neurologic deficits, or a combination thereof, but various tissues can be affected. This case highlights a unique presentation of protothecosis in a dog, in which lameness resulting from osteomyelitis was the predominant clinical sign. Key clinical message: Although osteomyelitis is an atypical manifestation, protothecosis can be a differential diagnosis for an aggressive bony lesion and is particularly worthy of consideration in immunocompromised dogs.