canine cutaneous mycobacterium avium subsp. avium infection

Almost inevitably, cutaneous mycobacteriosis develops after trauma through implantation (surgery and injection), or fulminates following wound contamination. sporadic m. avium subspecies avium (maa) infections are reported in humans and mammals. this report aims to describe localized pyogranulomatous panniculitis associated with maa in a 3-year-old male jack russell terrier with a history of cholestatic hepatitis and a subcutaneous non-painful and non-pruritic nodule after 2months post-vaccination. here we emphasize its clinical and pathological aspects along with molecular investigations, and provide the treatment protocol and outcomes. no additional cutaneous or subcutaneous lesions or lymphadenopathy were present upon clinical, radiographic, and ultrasonographic examinations, and hemogram and serum biochemistry were within normal limits. the mass was surgically excised and referred to surgical pathology service where the mass was macroscopically scrutinized and representative sections were routinely processed, sectioned, and stained with h&e method. as pathologically indicated, gram, acid-fast, and periodic acid schiff stainings and pcr for mycobacterial rpob gene and gene sequencing were utilized. macroscopically, a firm loculated tissue was seen in the hypodermis. histopathologically, extensive pyogranulomatous panniculitis (variably-sized circular-to-oval clear lipocysts, an outer rim of neutrophils, and an outer layer of foamy epithelioid cells, neutrophils, and minimal langhans form giant cells) was diagnosed. histopathologic findings were characteristic of mycobacteriosis, and special stainings ruled out other organisms. pcr and gene sequencing confirmed the initial histopathological diagnosis as infection with maa (ncbi, genbank accession number: oq656805). clarithromycin was avoided due to its potential cholestatic hepatitis adverse effects and marbofloxacin was administered for 2 weeks. nineteen months post-surgery the cutaneous lesions have not relapsed and the patient is clinically healthy. this study suggests that marbofloxacin monotherapy may be sufficient in immunocompetent dogs in cases of early detection of localized cutaneous mycobacteriosis and individuals lacking lymph node or organ involvement.