panniculitis in a cat from northern California.

Case Summary: A 9-year-old male castrated domestic shorthair cat from northern California was evaluated for a 12-month history of dermal and subcutaneous dermatitis in the inguinal region. Histopathologic examination of a biopsy revealed severe, chronic, multifocal to coalescing pyogranulomatous dermatitis and panniculitis, accompanied by ulceration and central necrosis. Aerobic bacterial culture of lesions yielded mycobacterial growth. Empiric antimicrobial therapy was initiated with doxycycline and marbofloxacin pending culture and susceptibility. Culture of a biopsy followed by gene sequencing at a mycobacterial reference laboratory yielded after 6 weeks. Ten months after initial antimicrobial administration, the lesions resolved.

Relevance And Novel Information: To date, in cats, panniculitis has been reported from Ohio, Massachusetts and British Columbia in North America; two additional cases were reported from southeastern Australia. In humans, infections have been reported from several states in the USA, predominantly in the Midwest and coastal south, but not from the west. This report extends the known spatial distribution of to the western USA and strengthens its association with panniculitis in cats. It also demonstrates the need for prolonged incubation for diagnosis of some rapidly growing mycobacteria infections using culture.