Rapid Cellular Growth in Dogs

Histiocytic Diseases in Dogs

Histiocytic disease are uncommon skin disorders resulting from rapid and excessive growth of cells. This cellular behavior is medically described as cell proliferation.

It occurs in young to middle-aged dogs, with a mean age of five years. There is no apparent gender predilection, and skin disease is not restricted to particular breeds, but systemic disease – where the skin disorder spread into the body system – has been reported predominantly in Bernese mountain dogs.

Symptoms and Types

Cutaneous histiocytosis

• Lesions involve skin and are subcutis (in the deep connective tissue of the skin)
• Multiple nodules or plaques on the head and neck, trunk, extremities, and scrotum
• No systemic organ involvement
• Often takes a fluctuating, chronic course, where spontaneous regression of lesions may occur

Malignant histiocytosis

• Pallor, weakness, shortness of breath (dyspnea) with abnormal lung sounds, and neurologic signs (e.g., seizures, central disturbances, back leg weakness)
• Moderate to severe enlargement of the lymph glands and enlargement of the spleen and liver
• Masses occasionally found in the liver and/or spleen
• Eyes and skin are rarely affected
• Malignant form affects older dogs, at a mean age of seven years
• Malignant histiocytosis is rapidly progressive and usually fatal

Systemic histiocytosis

• Marked tendency for skin, and lymph nodes
• Multiple cutaneous (outer skin) masses are nodular, well-defined, and often ulcerated, crusted or hairless around the mass (alopecic)
• Commonly found on the muzzle, nasal planum (black area of the nose), eyelids, flank, and scrotum
• Moderate to severe enlarged lymph glands (lymphadenomegaly) is often present
• Eye manifestations
• Abnormal respiratory sounds and/or nasal mucosa infiltration
• Organomegaly (organ enlargement) occurs with systemic involvement
• Systemic histiocytosis is a chronic and fluctuating debilitating disease with multiple clinical episodes and periods without symptoms

Other symptoms and types

• Most commonly affects Bernese mountain dogs
• Golden retrievers, flat coated retrievers, and rottweilers appear to be predisposed, suggesting genetic factors
• Lethargy
• Anorexia
• Weight loss
• Coughing
• Respiratory stertor (snoring sounds)
• Dyspnea (shortness of breath)
• Signs of systemic illness may not be present in dogs with cutaneous (skin) histiocytosis and in some dogs with systemic histiocytosis

Causes

• Systemic and cutaneous (outer skin) histiocytosis seem to result from inflammation of the cells
• Non-cancerous diseases arising from the expansion of activated skin cells
• Absence of infectious agents and responses to drugs suggest poorly regulated immune responses may be involved
• Malignant (aggressive and quickly spreading) proliferation of cells
• Familial disease of Bernese mountain dogs, accounts for up to 25 percent of all tumors in this breed

Diagnosis

Your veterinarian will perform a thorough physical exam on your dog, including a complete blood profile, chemical blood profile, a complete blood count, and a urinalysis. Extensive laboratory work will need to be essential for making a conclusive diagnosis. A biopsy (tissue and fluid sample) of the affected organs and/or lymph nodes will need to be collected, a cytologic examination (a microscopic examination of the cells) of bone marrow aspiration or biopsy may show systemic histiocytic infiltration. Diagnosis of histiocytosis is often difficult because the results of the microscopic analysis of the cells are not always definitive.

Immunohistochemistry, where a tissue sample is used for the detection of antigens (the molecules that bind to antibodies), typing the tumor and testing the tumor cell’s reaction to therapy, can be effectively used for diagnosing a histiocytic disease. Immunohistochemical staining may also be useful for verifying the histiocytic origin of cells.