related terms: systemic histiocytosis, malignant histiocytosis
Malignant and systemic histiocytosis are cancers characterized by the rapid and invasive spread of abnormal histiocytes - cells which are a type of macrophage. Macrophages arise from the bone marrow and circulate throughout the body as part of the normal defense system.
[A note on cutaneous histiocytosis: Cutaneous histiocytosis is a form of histiocytosis that is not inherited. It is quite rare and causes small skin lesions which may come and go, and may or may not respond to treatment. The histiocytes in the lesions are normal.]
How is histiocytosis inherited?
The disorder has a polygenic mode of inheritance.
What breeds are affected by histiocytosis?
Malignant and systemic histiocytosis occur most commonly in the Bernese mountain dog, accounting for approximately 25% of tumours in this breed. Histiocytosis occurs very rarely in other breeds as well.
For many breeds and many disorders, the studies to determine the mode of inheritance or the frequency in the breed have not been carried out, or are inconclusive. We have only listed breeds for which there is a strong consensus among those investigating in this field and among veterinary practitioners, that the condition is significant in this breed.
What does histiocytosis mean to your dog & you?
In both forms of histiocytosis, signs of illness include loss of appetite, weight loss, and lethargy. In systemic histiocytosis, there are striking skin lesions (crusting, firm nodules, ulcers) but these are uncommon in malignant histiocytosis.
Malignant histiocytosis usually occurs in middle-aged or older dogs while the systemic form may affect younger dogs. There may be prolonged periods of remission with systemic histiocytosis, but ultimately the histiocytes infiltrate other organ systems especially the lungs, liver, spleen, bone marrow, and lymph nodes. Malignant histiocytosis is a rapidly progressive and invasive disorder, which commonly metastasizes to the lungs.
How is histiocytosis diagnosed?
The clinical signs of this disorder vary depending on where metastasis of abnormal cells occurs. Tumours in the lungs are common, causing respiratory signs such as coughing and shortness of breath. Your veterinarian will likely suspect a tumour based on clinical signs, radiology, and blood tests; he or she will submit tissue samples to a pathologist for histopathologic examination to determine the type of tumour.
For the veterinarian:
CLINICAL: most common in Bernese mountain dogs; see anorexia, weight loss, lethargy, lymphadenopathy, plus signs associated with metastasis (commonly respiratory, also gastrointestinal or nervous); with systemic histiocytosis, you will also see multiple cutaneous plaques, ulcers, nodules and papules, which can be anywhere but are seen primarily on face and limbs.
RADIOLOGY: commonly see thoracic abnormalities such as single or multiple masses, hilar lymphadenopathy, pleural effusion; may see hepato or splenomegaly.
LABORATORY: hematology may be normal, or there may be regenerative or non-regenerative anemia; may see elevated liver enzymes; cytologically, the histiocytes of malignant histiocytosis are abnormal, while those of systemic histiocytosis appear normal.
Malignant histiocytosis spreads rapidly and metastasis is generally present at the time of diagnosis, so that surgical treatment is ineffective. Dogs with systemic histiocytosis may experience prolonged periods of remission, or the disease may progress rapidly. Various types of chemotherapy have been tried for both types of histiocytosis, but with little success.
Your veterinarian will work with you to keep your dog as comfortable as possible, until the quality of life deteriorates to the point where euthanasia is the best treatment option.
Because this invariably fatal disorder generally does not develop until the dog is middle-aged or older, it can be hard to identify parents that carry the trait. It is very important that the veterinarian and/or owner inform the breeder when this disorder has been diagnosed, so that he or she can modify the breeding programme accordingly, to limit the spread of the harmful gene(s) in the Bernese mountain dog population.
FOR MORE INFORMATION ABOUT THIS DISORDER, PLEASE SEE YOUR VETERINARIAN.
Panic, R. 1992. Sterile pyogranulomatous and granulomatous disorders of dog and cats. D. Bonagura and R.W. Kirk (eds.) Kirk's Current Veterinary Therapy XI Small Animal Practice, p. 536-539. W.B. Saunders, Toronto.
Copyright © 1998 Canine Inherited Disorders Database. All rights reserved.
Revised: October 30, 2001.This database is funded jointly by the Animal Welfare Unit at the Atlantic Veterinary College, University of Prince Edward Island, and the Canadian Veterinary Medical Association.