Dogs afflicted with malignant histiocytosis may show pallor, weakness, dyspnea with abnormal lung sounds and neurologic signs,
such as seizures, central disturbances and posterior paresis.
Moderate to severe lymphadenomegaly and hepatosplenomegaly may be present. Occasionally, masses are palpated in the liver
and/or spleen. Eyes and skin are rarely affected.
The CBC commonly shows a mild to severe anemia (regenerative or nonregenerative) and thrombocytopenia. The serum chemistry
profile results may reflect the degree of organ involvement.
Thoracic radiographs may show well-defined, nodular pulmonary opacities, pleural effusion, lung lobe consolidation, diffuse
interstitial infiltrates, mediastinal masses, and sternal and bronchial lymphadenomegaly. Abdominal radiographs often show
hepatomegaly, splenomegaly and abdominal effusion. Biopsy of affected organs and/or lymph nodes is helpful in confirming the
diagnosis. Cytologic examination of bone marrow aspirate or biopsy may show histiocytic infiltration.
Fluid therapy or blood transfusions may be required depending on clinical findings. Palliative therapy with corticosteroids
may be helpful for about four to 18 months. Dogs diagnosed with systemic disorder have a fluctuating debilitating disease
that can be characterized by multiple clinical episodes and asymptomatic periods. Prognosis for malignant disorder is extremely
poor; death usually occurs within a few months of diagnosis.