Clinical History
A 3 year old female spayed Cairn terrier was presented to the Veterinary Medical Teaching Hospital, Colorado State University with a 4-5 month history of lethargy, difficulty rising and a stiff-stilted gait. Thoracic and abdominal radiographs were taken and no abnormalities identified, with the exception of possible narrowing of one of the thoracic disk spaces. Treatment trials of prednisone and carprofen were initiated and seemed to help, however, the owner was reluctant to continue administering prednisone without a diagnosis. Hermione declined on carprofen twice daily and acupuncture weekly, and a 2 kg weight loss was reported. Disk disease was suspected and Hermione was evaluated by the soft tissue surgery service for a second opinion regarding a hemilaminectomy.

Physical and Neurological Examination
After initial evaluation, it was determined that the problem was not surgical and Hermione was transferred to the Internal Medicine Service. On physical examination, the dog had a body condition score of 3/9 and was febrile (103.8°F), with a normal heart and respiratory rate. Femoral pulses were strong bilaterally. On rectal examination, significant pain was elicited upon palpation of the lumbosacral joint. Orthopedic examination revealed enlarged, warm and painful joints bilaterally in the carpi, tarsi, stifles and elbows. Pain was also elicited on extension and flexion of the coxofemoral joints. Generalized muscle wasting was observed with severe wasting of the muscles of mastication and proximal limbs. The gait was stiff and stilted with difficulty rising from a sitting position. Neurological examination was normal with the exception of weak withdrawals in all limbs. A presumptive diagnosis of polyarthritis with or without a concurrent neuromuscular disease was made.

Diagnostic Testing
CBC – A normal mature neutrophil count with a left shift was found along with a microcytic, normochromic, non-regenerative anemia with moderate keratocytes. These findings were consistent with chronic gastrointestinal hemorrhage and resultant iron deficiency anemia.

Chemistry Panel – Elevated creatine kinase (CK, 551 IU/L, reference 50-275),  aspartate aminotransferase (AST, 207 IU/L,  reference 16-50) and alkaline phosphatase (ALP, 478 IU/L, refererence 20-142) were identified.  Based on these findings, muscle damage was suspected. The elevated ALP was consistent with steroid administration.

Arthrocentesis – Multiple joint taps revealed marked suppurative inflammation in the right carpus, tarsus and stifle joints. The cellularity was moderately to markedly increased and consisted almost entirely of nondegenerate neutrophils and rare large mononuclear cells. No organisms were observed. Aerobic and anaerobic cultures of the synovial fluid, and cultures for mycoplasma, were negative. The findings were consistent with an immune-mediated arthropathy.

Radiography – Radiographs of the carpi and tarsi showed soft tissue and joint capsule swelling but no evidence of erosive changes.

Muscle Biopsy – Muscle biopsies were collected under general anesthesia from the triceps and  biceps femoris muscles. Unfixed biopsies were refrigerated and shipped by an express service to the Comparative Neuromuscular Laboratory where they were immediately flash frozen in isopentane pre-cooled in liquid nitrogen then evaluated in frozen sections (Link to December 2006 Special Feature). Fixed biopsies were immersed in 10% buffered formalin and paraffin embedded. Mild to moderate inflammatory myopathy/myositis without fiber loss or fibrosis was evident in  both muscles.Mononuclear cell infiltrates were composed of lymphocytes (Fig. 1) and acid phosphatase positive macrophages (Fig. 2). An immune-mediated (polymyositis) or collagen-vascular disorder  was suspected based on the clinical presentation. Infectious  causes of myositis including Toxoplasma,  Neospora and tick-related  disorders were ruled out.

Treatment and Outcome
The final diagnosis was a polyarthritis-polymyositis syndrome of immune origin. Prednisone was initiated at 20mg divided BID for two weeks with a slow taper, azathioprine 12.5 mg SID, and tramadol (25 mg PO QID), famotidine (5 mg PO BID) and sucralfate (500 mg PO in a slurry one hour prior to other medication) as gastroprotectants. A few days after discharge the owner noted that Hermione was feeling much better, was more active, walking faster and actually running down the stairs.