Systemic histiocytosis: Dogs may not show signs

Signalment

Canine, Bernese Mountain dog, 9 years old, female spayed, 70 lbs.

Clinical history

The dog presents for lethargy and decreased appetite for the last one to two weeks. Therapy is pending.

Image 1.

Physical examination

The findings include rectal temperature 101.6° F, heart rate 150/min, respiratory rate 45/min, pale mucous membranes, normal capillary refill time, normal heart sounds and coarse lung sounds. The dog has had weight loss of 9 lbs. in the past two months and now has a palpable abdominal mass.

Laboratory results

A complete blood count, serum chemistry profile and urinalysis were performed and are in Table 1.

Table 1.

Radiograph examination

The lateral thoracic radiographs are normal. The lateral abdominal radiograph shows an enlarged soft tissue mass in the mid-abdomen.

Image 2.

Ultrasound examination:

Thorough abdominal ultrasonography was performed. The dog was positioned in dorsal recumbency for the ultrasonography.

My comments:

The liver shows a mixed echogenicity in its parenchyma. There are several echobright areas in the liver parenchyma. No masses noted within the liver parenchyma.

Image 3.

The gall bladder is mildly distended, and its walls are not thickened or hyperechoic. The gall bladder does contain some sludge material. The spleen is irregularly enlarged and shows mixed echogenicity in its parenchyma.

There are multiple hyperechoic masses present within the splenic parenchyma. Only one cavitated lesion noted in the splenic images provided. The left and right kidneys are similar in size, shape and echotexture. No masses or calculi were noted in either kidney. The urinary bladder is distended with urine and contains some urine sediment material - no masses or calculi noted. The stomach and pancreas appear to be normal.

Image 4.

Case management:

In this case, intra-abdominal neoplasia is the clinical diagnosis. Beware of malignant histiocytosis of Bernese Mountain dogs. At this point, an exploratory laparotomy would be warranted to confirm the presence of neoplasia, excise the abnormal spleen, inspect the abdominal cavity for potential metastatic disease and collect appropriate biopsies for histopathologic examination. Therapy, thereafter, would depend on the findings from the exploratory laparotomy and histopathologic examination.

Malignant histiocytosis

Histiocytosis results from proliferation of cells from the monocyte-macrophage lineage and often affects the skin and hemic, lymphatic, nervous, ophthalmic and/or respiratory system. Young to middle-aged, average age at onset is 4 years, male Bernese mountain dogs are affected with systemic histiocytosis; older male Bernese mountain dogs are affected with malignant histiocytosis.

Image 5.

Familial disease of Bernese mountain dogs is inherited by polygenic mode; heritability is 0.298; and accounts for up to 25 percent of all tumors in this breed. Dogs with systemic histiocytosis may not have any signs of systemic illness.

Dogs that do may show cutaneous masses - multiple, nodular, well-circumscribed and often ulcerated, crusted or alopecic - of the muzzle, nasal planum, eyelids, flank and scrotum; moderate to severe peripheral lymphadenomegaly; ocular manifestations - conjunctivitis, chemosis, scleritis, episcleritis, episcleral nodules, corneal edema, anterior and posterior uveitis, retinal detachment, glaucoma and exophthalmos; abnormal respiratory sounds and/or nasal mucosa infiltration; and organomegaly.

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.

Image 6.

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.