Systemic histiocytosis of Bernese mountain dogs

A histiocytic proliferative disorder was identified in six closely related Bernese mountain dogs. Clinical signs included anorexia, weight loss, stertorous respiration, and conjunctivitis with marked chemosis. Multiple cutaneous nodules were distributed over the entire body but were especially prevalent in the scrotum, nasal apex, nasal planum, and eyelids. Lesions consisted of perivascular infiltrates of large histiocytes as well as minor populations of lymphocytes, neutrophils, and eosinophils. Histiocytes were further characterized by enzyme histochemistry and electron microscopy. Necropsy examinations of four dogs revealed that the histiocytic infiltrates were widespread and involved skin, lung, liver, bone marrow, spleen, lymph nodes, kidneys, testes, orbital tissues, and others. However, skin and peripheral lymph nodes were more consistently involved. The disease course was punctuated by remissions and relapses not clearly influenced by conventional therapeutic measures. Preliminary results of an experimental therapeutic regimen involving administration of bovine thymic extracts in two dogs are present. The relationship of the disorder to other human and canine histiocytic proliferative disorders is discussed.