Polymyositis has been described as a manifestation of canine SLE, but a non-lupoid syndrome of polyarthritis and polymyositis
has been described.1,4,16,20
The syndrome occurs most commonly in young to middle-aged spaniel breeds.4
Dogs present with waxing and waning stiffness, joint effusion, myalgia, muscle contracture, and progressive bilaterally symmetric
muscle atrophy.1,4,16,20 Treatment is similar to that of idiopathic IMPA, but the presence of concurrent muscle involvement worsens the prognosis,
and response to treatment is variable.16,20
IMPA has been associated with the administration of a variety of medications, including sulfonamides, lincomycin, erythromycin,
cephalosporins, phenobarbital, and penicillins.1,2,4 Sulfonamides, including sulfadiazine, sulfamethoxazole, and sulfadimethoxine, are most commonly implicated.21-24 Polyarthritis induced by sulfonamides is most notable in Doberman pinschers and other large breeds and occurs at recommended
Signs of polyarthritis occur, on average, five to 20 days after drug exposure.21-24 With previous exposure, signs may occur more rapidly.21-24 Clinical signs are typical of IMPA (e.g. lameness, swollen and painful joints, fever, and lymphadenopathy) and may occur with concurrent hypersensitivity reactions
including thrombocytopenia, hepatopathy, neutropenia, keratoconjunctivitis sicca, hemolysis, uveitis, or skin and mucosal
Treatment involves discontinuing the drug; improvement in polyarthritis generally occurs within 24 hours.21-24 Complete recovery generally occurs within two to five days of drug withdrawal. Some cases require immunosuppressive therapy
for quicker and more complete resolution of clinical signs. The reported prognosis is generally good.
Vaccines have been implicated as an inciting event for IMPA but such cases are poorly documented within the veterinary literature.1,4,5,15,25 In reported cases, IMPA caused by vaccines occurred within 30 days of vaccination. A true cause-and-effect relationship
is difficult to prove, and little is known about a potential pathophysiologic mechanism. Canine distemper antigens have been
found in immune complexes from joints of dogs with erosive IMHA and may suggest vaccine involvement.16 Most vaccine-associated IMPA cases are self-limiting and may require a short course of immunosuppressive treatment.
Breed-specific cases of nonerosive IMPA include syndromes observed in Akitas and Chinese Shar-Peis.
A rare, nonerosive polyarthritis affects adolescent Akitas and may occur concurrently with meningitis or other organ involvement.16,26 Affected dogs are treated with immunosuppressive agents, but response is generally poor.
Shar-Peis can experience a polyarthritis syndrome known as Shar-Pei fever or swollen hock syndrome.1,2,16 It is an autosomal recessive disease associated with elevated interleukin-6 production.1 The age of onset is variable, and the syndrome typically presents as cyclical episodes of fever and joint swelling of one
or both hocks.1,2 Joint swelling may be due to effusion or periarticular swelling, and enthesopathies (abnormalities involving the tendon
or ligament attachments to bone) may be present.1,2 Amyloidosis can be a component of the disease and occurs independent of fever and joint swelling.1,2
These cyclical episodes may require palliative treatment but can spontaneously resolve. Treatment of amyloidosis has been
attempted with colchicine, but no studies have proved its efficacy.1,2 Prognosis is variable depending on the degree of amyloidosis, and renal or liver failure is often the cause of death.1,2