Mycobacterium avium-complex infection mimicking lymphoma in a miniature schnauzer

This case report describes an uncommon Mycobacterium avium infection mimicking lymphoma in a dog.

A 1.5-year-old female Miniature Schnauzer presented with persistent lymphadenopathy, fever, and diarrhea, which were refractory to conventional therapy. Hematological and biochemical analyses revealed anemia, thrombocytopenia, elevated liver enzymes, creatine kinase, glutamate dehydrogenase, lactate dehydrogenase, hyperkalemia, low IgG levels, and euthyroid sick syndrome. Ultrasonography confirmed generalized visceral, retroperitoneal, and peripheral lymphadenopathy with concurrent inflammatory reactions, splenomegaly, and hepatomegaly characterized by heterogeneous parenchyma and multiple foci, further supporting the suspicion of lymphoma. However, cytological examination of an enlarged lymph node showed no evidence of lymphoma but revealed the presence of numerous bacilli suggestive of mycobacterial infection. Histopathological evaluation of a surgically excised lymph node similarly failed to confirm lymphoma. Mycobacterium avium was successfully cultured from the lymph node tissue and identified via the GenoType Mycobacterium CM test. Based on antimicrobial susceptibility testing, the initial therapeutic regimen of enrofloxacin, azithromycin, and rifampicin was modified to clarithromycin. Adjunctive treatments included blood transfusion, levothyroxine, prednisolone, omeprazole, sucralfate, parapoxvirus ovis, and soy phospholipids. Despite a temporary clinical improvement, the patient's condition progressively worsened, and the dog succumbed to the disease after three months.

This case underscores the importance of including Mycobacterium avium in the differential diagnosis of generalized lymphadenopathy, particularly in Miniature Schnauzers. The findings support the routine use of Ziehl-Neelsen staining during cytological examinations to prevent misdiagnosis, especially in breeds predisposed to atypical infections. It also emphasizes the crucial role of targeted antimicrobial therapy in managing such cases, although the prognosis remains guarded.