Benign histiocytomas are common in dogs. They form skin lumps that do not metastasize and sometimes go away by themselves. Early symptoms of histiocytosis include depression, lethargy, loss of appetite and weight loss. With systemic histiocytosis skin abnormalities are common, particularly on the face and limbs. If the tumor has metastasized to the lungs there may be trouble breathing.
Anemia is also common.
X-rays may indicate internal masses and other abnormalities. Histopathology can help differentiate between the malignant and systemic forms. Malignant histiocytosis progresses rapidly and has usually metastasized by the time it is diagnosed. Systemic histiocytosis may under go several remissions or none at all before finally affecting internal organs. In all cases owners should observe their dogs quality of life closely to determine the appropriate time for euthanasia.