Cutaneous mycobacteriosis caused by Mycobacterium avium subspecies avium in a dog: Clinical findings, histopathological and molecular diagnosis and treatment

Abstract

AbstractA 3‐year‐old castrated male Jack Russell Terrier with a history of cholestatic hepatitis was presented with a non‐painful and non‐pruritic, subcutaneous nodule following vaccine injection. The dog was otherwise healthy. The nodule was surgically removed. Upon gross inspection, a firm, glistening and loculated tissue was seen within the panniculus. Histopathologically, extensive pyogranulomatous panniculitis was diagnosed, composed of variably sized lipocyst surrounded by neutrophils and an outer zone of foamy epithelioid macrophages, neutrophils and occasional Langhans form giant cells. Although histopathologic findings were most compatible with mycobacteriosis, other infectious and sterile conditions were considered differential diagnoses. Gram, acid‐fast and periodic acid Schiff staining were negative. However, PCR analyses for mycobacterial rpoB gene and sequencing revealed infection with Mycobacterium avium subsp. avium. Empirical treatment was avoided through the 3‐week course of histopathological and molecular investigations. Considering that there were no newly formed cutaneous masses, marbofloxacin (2 mg/kg, PO q24h) was administered for 2 weeks, and clarithromycin was avoided due to its potential cholestatic hepatitis adverse effects. Eight months following surgery, there are no new or relapsing cutaneous lesions or disease‐specific complications. This suggests that marbofloxacin monotherapy may be sufficient in immunocompetent dogs with early detection of localized cutaneous mycobacteriosis lacking lymph node or organ involvement.