MALIGNANT HISTIOCYTOSIS OF THE DOG - 26 C ASES (1989-1992)

Malignant histiocytosis is a malignant, progressive disorder character ised by the multisystemic proliferation of morphologically atypical hi stiocytes. Malignant histiocytosis was diagnosed in 26 dogs admitted t o the Veterinary Hospital of the Veterinary Faculty of the University of Zurich between 1989 and 1992. The age of the patients ranged from 3 to 12 years and the male to female ratio was 1:1. 19 dogs (73 %) were purebred or mixed Bernese Mountain Dogs. Among the nonspecific clinic al signs, anorexia, lethargy, weight loss, weakness, pale mucous membr anes, fever, vomiting and lymphadenopathy predominated. Frequent findi ngs in hematology and serum biochemistry were regenerative anemia (10) , lymphopenia (12), monocytosis (7), leukocytosis (6), thrombocytopeni a (6) and increased liver enzymes, BUN and creatinine. Radiography and ultrasonography were helpful in localising the disease and assessing its extent. On thoracic radiographs pulmonary masses (9), cranial medi astinal masses (8), hilar masses (6), and enlarged sternal lymph nodes (5) were the predominating findings. Abdominal radiography and ultras onography frequently revealed hepatomegaly (14), splenomegaly (10), ma sses or hypoechoic zones in the spleen (11) and in the liver (6) and e nlarged abdominal lymph nodes (8). Cytology (aspiration of masses in t he thorax or abdomen and of enlarged lymph nodes, bone marrow examinat ion), liver biopsy and exploratory laparotomy were important diagnosti c aids. In 22 dogs necropsy was performed and the clinical pathologica l diagnosis was confirmed in every case. Lymph nodes (1 8), spleen (1 3), lung (1 2), liver (11), kidneys (8), bone marrow (7) and mediastin um (6) were the most frequently involved organs.