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Case Report: Polyarthritis and meningitis in a nine month old Basset Hound

 Signalment, history and physical examination

A nine month old male entire Basset Hound was presented with a three week history of lethargy, pyrexia and anorexia that had been unresponsive to treatment with amoxicillin-clavulanate and meloxicam. On initial presentation the dog was quiet but alert. The only abnormal findings on clinical examination were mild enlargement of the popliteal lymph nodes and mild discomfort on manipulation of the elbows and shoulders.

Differential diagnoses

Lethargy and anorexia are non-specific signs that were likely to be secondary to the underlying problem. The main differentials considered for pyrexia were infection, inflammation, immune-mediated disease, neoplasia, toxins and tissue necrosis. The popliteal lymphadenopathy may have resulted from local inflammatory disease (eg. arthritis, dermatitis, lymphadenitis, metastatic neoplasia) but a systemic condition resulting in lymphadenopathy (eg. lymphoma, systemic infection) could not yet be ruled out. Discomfort on manipulation of the joints is suggestive of arthritis and immune-mediated, infectious, traumatic, degenerative or neoplastic aetiologies should be considered.

Initial investigation

Blood and urine were taken to investigate the possibility of inflammatory or infectious disease.  However, since the dog had recently received NSAID therapy and was not currently pyrexic he was discharged and asked to return the following week. Urinalysis was unremarkable. Routine haematology revealed marked neutrophilia that was most likely due to infection or inflammation. Serum biochemistry revealed mild hyperglobulinemia in association with mild hypoalbuminemia, which was likely to be a result of ongoing inflammation resulting in an acute phase response. A low creatinine was likely to be a reflection of low muscle mass and the elevations in calcium and phosphate were likely to be age related.  

Further investigation

fig.1 - mediolateral radiograph of right elbow

Five days later the dog became depressed and lethargic. His neck carriage was low, his gait was hunched with stiff hindlimbs and discomfort was noted on manipulation of the cervical and lumbar spine. The remainder of the clinical examination was as previously but pyrexia was now present (39.9oC). Full neurological examination was unremarkable. Intravenous fluid therapy was instigated and Tramadol was given for analgesia.

Screening for borrelia, bartonella and ehrlichia was negative, as was antinuclear antibody and rheumatoid factor serology. Thoracic and abdominal radiography was unremarkable as was abdominal ultrasonography. Spinal radiographs were unremarkable and, given the chronicity of the problem, this made discospondylitis unlikely. Gross conformational abnormalities were evident in the elbow and stifle radiographs (figures 1 & 2) but no joint effusions or reactive changes were noted. However, this would not exclude an inflammatory arthritis and neutrophilic inflammatory changes were noted on cytology of the synovial fluid from the right stifle and left carpus. Aerobic and anaerobic bacterial culture of synovial fluid was negative. Cytology of the popliteal lymph nodes was unremarkable. Csf cytology revealed a markedly elevated cell count and high protein levels consistent with meningitis.

fig.2 - mediolateral view of right stifle

The clinical signs and laboratory findings were indicative of meningitis with concurrent non-erosive polyarthritis. There was no evidence of underlying infectious, inflammatory or neoplastic disease and drug reaction was excluded given the lack of history of recent drug exposure or vaccination prior to disease onset. A primary immune-mediated meningitis-arthritis syndrome was therefore most likely.

Management and follow up

Treatment with immunosuppressive doses of prednisolone (1mg/kg po bid) was started along with gastroprotectants (sucralfate 1g po tid). This resulted in a marked improvement in demeanour and reduced neck pain. However, a markedly stiff gait remained. The prednisolone dose was gradually increased to 2mg/kg twice daily and azathioprine therapy (2mg/kg po eod) was added with weekly monitoring of the haematology. The dog continued to make steady improvement over the next few weeks and drug therapy was slowly tapered and withdrawn over the following six months. Two months following cessation of therapy the dog remains asymptomatic.

Discussion

Spinal pain is a common finding in dogs with immune-mediated polyarthritis (IMPA), identified in ~29% of cases. In almost half of these dogs the spinal pain is found to be a result of concurrent steroid responsive meningitis (SRM). Previously, certain breeds (including Beagles, Bernese Mountain Dogs, Boxers and Akitas) have been found at increased risk of this polyarthritis-meningitis syndrome, but more recent studies suggest that any breed can be affected. It is thus advisable that any dog with IMPA and spinal pain has csf analysis performed. SRM has also been described in association with polymyositis/polyarthritis but the lack of elevation in creatine kinase or aspartate aminotransferase made this syndrome unlikely in this case. There were no other clinical signs consistent with polyarteritis nodosa such as skin or mucous membrane ulceration and the lack of other apparent immune pathology with a negative ANA titre excluded SLE as a differential.

Although septic arthritis is usually monoarticular, definitive exclusion can be difficult. Synovial fluid cytology can be similar in sepsis and immune-mediated diseases and culture of synovial fluid can yield false negative results. However, sepsis was considered extremely unlikely in this case, particularly given the good response to immunosuppressive therapy. Similarly, SRM with an unrelated rheumatoid arthritis could initially not be definitively excluded since erosive changes are not always present early in the course of disease and some dogs have a negative RF titre. However, given the age of the dog, the waxing and waning nature of the abnormal gait this was considered unlikely.

As was the case in this patient, dogs with IMPA rarely have grossly observable swollen joints and may not present with obvious signs of lameness. In contrast, non-specific signs of pyrexia and lethargy are common. Synovial fluid analysis is therefore an important investigative tool in cases of pyrexia of unknown origin and, since it is rare for all joints to be affected, multiple joints should be tapped.

Although the treatment for dogs with IMPA and SRM is similar, it is still important to ascertain whether SRM is present because dogs which are inadequately treated for SRM are at risk for the development of neurological damage, which can be permanent. As in this case, response to immunosuppressive therapy can be excellent with chemotherapeutic immunosuppression resulting in complete cure in 56% of dogs. However, recurrence is not uncommon and the owners were therefore advised to observe the dog carefully for early signs of recurrence.