Challenging diagnosis and successful treatment of localised <i>Mycobacterium avium</i> subsp. <i>hominissuis</i> glossitis in a dog on long-term immunomodulatory therapy

Case history A 3-year-old, intact female mixed-breed dog, weighing 7 kg, was presented with generalised swelling of the tongue, leading to impaired deglutition and episodes of dyspnoea. From the age of 2 years, the dog had been under immunosuppressive therapy due to atopic dermatitis.Clinical findings and treatment Multiple nodular lesions at the apex of the tongue were noted as well as mandibular and retropharyngeal lymph node enlargement. Serum biochemistry results showed inflammatory changes. The results of several biopsies taken over 7 months indicated persistent pyogranulomatous and necrotising glossitis despite ongoing antimicrobial treatment, first with amoxicillin/clavulanic acid and then pradofloxacin. No foreign material, acid-fast bacteria or fungal hyphae were detected throughout. The final diagnosis of Mycobacterium avium subsp. hominissuis (Mah) was reached after PCR and bacterial culture were carried out on the third biopsy sample. Therapy was initiated with rifampicin, clarithromycin and doxycycline, leading to complete remission of the lesions.Diagnosis Severe chronic pyogranulomatous and necrotising glossitis associated with infection by Mah.Clinical relevance This report describes challenges in the diagnosis and therapy of a localised Mah infection in an iatrogenically immunocompromised dog. Successful treatment was only achieved with a specific combination of antibiotics administered long-term.Abbreviations AF: Acid-fast; ALP: Alkaline phosphatase; CT: Computed tomography; MAC: Mycobacterium avium complex; Mah: Mycobacterium avium subsp. hominissuis