Clinical Case Challenge: Canine Fever with Shifting Leg Lameness and Travel History

By Orla Mahony and Florian Wuillemin

A 1-year-old Labrador retriever had fever, lethargy, and shifting leg lameness.

On presentation to the Henry and Lois Foster Hospital for Small Animals, the dog had bilateral mucopurulent ocular discharge, a normal temperature, mildly enlarged popliteal lymph nodes, and generalized musculoskeletal discomfort with pain on palpation of the midback and elbows.

History

A 1 -year-old castrated male CM Labrador retriever presented for fever (temperature 103.3 to 105.4), lethargy, and shifting leg lameness. The dog was adopted from Texas and had spent time in Oklahoma. He was fully vaccinated. A workup had shown leukocytosis (42,000 WBC), neutrophilia, monocytosis, two negative 4dx tests, a negative fever of unknown origin realPCR panel (anaplasma spp, ehrlicihia spp, babesia spp, rickettsia spp, canine bartonella, brucella canis, cryptococcus spp, neospora caninum, toxoplasma gondii), and the presence of isospora on a fecal. Treatments included amoxicillin, albon, carprofen, and doxycycline, with a partial response, especially to carprofen. Can you solve the case of the month?

On presentation to the Foster Hospital, the dog had bilateral mucopurulent ocular discharge, a normal temperature, mildly enlarged popliteal lymph nodes, and generalized musculoskeletal discomfort with pain on palpation of the midback and elbows.

Determine which additional diagnostics are required

• A urinalysis and culture were negative.
• Radiographs were taken of the left forelimb and thoracolumbar spine and showed no abnormalities.
• A CBC showed 54,000 WBC with neutrophilia and monocytosis. A chemistry profile showed a mildly elevated ALP liver enzyme.
• A buffy coat preparation was negative for infectious organisms and overtly neoplastic cells. A PCR test for hepatozoonosis was submitted and came back negative.

What is the next step for this patient?

Because carprofen might have been masking signs, it was discontinued for three days and he was readmitted for further evaluation.

Physical exam revealed fever (104), normal ambulation with no apparent joint effusion, discomfort on palpation of his mid back, and mucopurulent ocular discharge, with mild entropion. A Schirmer’s tear test was slightly decreased.

There are many rule-outs for fever. Diseases considered for this patient were infectious (tickborne disease, fungal, discospondylitis, bacterial endocarditis), inflammatory (immune mediated polyarthritis, polymyositis, meningitis, panosteitis), and neoplastic (leukemia, paraneoplastic syndrome).

Because neutrophilia and shifting leg lameness are highly suggestive of hepatozoonosis the decision was made to repeat the PCR test. Blood was submitted to Auburn and returned positive for Hepatozoon americanum, a species of protozoa that can cause hepatozoonosis, a debilitating, potentially fatal disease. Treatment was begun with a two-week course of trimethoprim-sulfadiazine, clindamycin, and pyrimethamine followed by long-term therapy with a coccidiostat, decoquinate. The patient is currently on his fifth month of treatment and doing very well.

Comments from Cummings School’s Internal Medicine Team

“Exotic” infectious diseases such as hepatozoonosis are more common now in New England as dogs are increasingly adopted from the Southern United States. Hepatozoonosis is an important consideration for dogs with a markedly high white cell count. False negative tests can occur with any disease, and whenever a clinician has a high index of suspicion, repeat testing is recommended.

To read more about this disease see the Companion Animal Parasite Council.

Dr. Orla Mahony is a clinical assistant professor in internal medicine at Cummings School of Veterinary Medicine at Tufts University. She is board-certified by both the American and European Colleges of Veterinary Internal Medicine.

Dr. Florian Wuillemin is a resident in internal medicine at Cummings School of Veterinary Medicine at Tufts University.