Histiocytosis is a general name for a group of syndromes. These syndromes all include an abnormal increase in the number of certain immune cells, called histiocyte cells. Histiocyte cells include monocytes, macrophages, and dendritic cells. The abnormal increase in the number of these immune cells may lead to the development od tumors in various parts of the body. The Bernese Mountain Dog is particularly prone to a malignant skin condition called cutaneous histiocytosis which resembles malignant histiocytosis of man (disseminated histiocytic sarcoma), where the disseminated form of histiocytic sarcoma accounts for up to 25% of deaths in the breed. Histiocytosis occurs most commonly in dogs between three to eight years of age. In flat-coated retrievers localised lesions most commonly develop in the deep musculature of the limbs or the elbow. Even these localised lesions are highly malignant with rapid dissemination to lymph nodesand the skin in over 70% of cases. The disease is rapidly progressive and fatal; many dogs are euthanized upon diagnosis; survival time from diagnosis has been reported to be 49 days. Treatment with Lomustine (CCNU) has been reported to result in some short term responses. The striking high incidence of histiocytic sarcoma in these breeds of dog suggests a heritable predisposition. A recent study of Danish Bernese mountain dogs described 13 dogs diagnosed with malignant histiocytosis, of which 11 were genealogically related.
Dogs develop fairly large red plaques or nodules in the skin (1 to 5 cm diameter). The lesions seem to wax and wane and appear in new sites, regardless of treatment. Lymph nodes, liver, spleen, and central nervous system are also frequently involved in which case dogs often develop systemic histiocytosis affecting the whole body. Affected animals often lose weight, have trouble breathing, anemia, coughing, lethargy, and conjunctivitis. Diagnosis is made by visual examination and biopsy. The disease course is characterized by remissions and relapses not clearly influenced by conventional therapeutic measures. In systemic histiocytosis, treatment with glucocorticoids and cytotoxic immunosuppressive drugs may help in the mildest cases. Histiocytosis does not respond well to chemotherapy, and the condition is usually fatal.
Benign cutaneous histiocytoma is a skin tumor with a round, raised, hairless, and often red appearance. This type of histiocytomas is the proliferation of epidermotropic Langerhans cells and most often occurs in young dogs between 1 and 3 years old. Some histiocytomas will shrink and eventually disappear following topical treatment with corticosteroid drugs. Treatment for benign and for solitary and non-numerous multiple nodules include surgery, electrosurgery and cryotherapy, usually with excellent prognosis.
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