Masticatory and skeletal muscle myositis in canine leishmaniasis (Leishmania infantum)

Twenty-four dogs with a parasitologically and serologically established dia gnosis of leishmaniasis were studied to investigate the atrophy of the mast icatory muscles which commonly occurs in this disease, and to compare the l esions in the masticatory muscles with those in the cranial tibial muscles. The 24 animals were divided into three groups of eight, group A dogs with no muscular atrophy, group B dogs with different degrees of atrophy in the masticatory and skeletal muscles, and group C dogs with similar degrees of atrophy in the masticatory and skeletal muscles. Increased activities of cr eatine phosphokinase and lactate dehydrogenase were recorded in only some o f the dogs in groups B and C, but there were no significant differences bet ween the mean activities in the three groups. Electromyographic changes ind icating myopathy and involving both the temporalis and cranial tibial muscl es, were observed in two of the dogs in group A, seven of those in group B. and in all the dogs in group C. Muscle histopathology revealed a variable degree of muscle fibre necrosis and atrophy, mononuclear infiltrates and ne utrophilic vasculitis in all the dogs except two in group A. Leishmanial am astigotes were found within macrophages and myofibres in 16 of the dogs, so me in each group. IgG immune complexes were detected in muscle samples, and circulating antibodies against myofibres were detected in serum samples fr om all the 24 dogs.