antibiotic, helps distinguish serum sickness from other causes of polyarthritis and fever Kawasaki disease is characterized by high and persistent fever, conjunctival injection without exudate, mouth and lip swelling and cracking, swelling and erythema of the hands and feet, a nonspecific rash, and lymphadenopathy About 30% of patients will also develop arthritis or arthralgia, with about one-third of these having onset in the first 10 days of illness Daily temperature spikes exceeding 40°C, especially if accompanied by a transient pink rash, suggest systemic-onset juvenile rheumatoid arthritis (JRA), one of the categories of juvenile idiopathic arthritis (JIA) A common viral-related arthritis is that caused by hepatitis B infection The arthritis precedes the symptoms of hepatitis and resolves when the jaundice appears Parvovirus B19 is the causative agent of erythema infectiosum; about 5% of affected children will complain of transient, bilateral joint swelling Joint manifestations due to this virus can also occur in the absence of a rash causing a sudden onset of symmetric, self-limited polyarthritis, particularly in the hands With subacute bacterial endocarditis, musculoskeletal symptoms are variable, ranging from asymptomatic joint effusions to frank arthritis of up to three joints Pre-existing congenital heart disease, a prolonged fever, a new murmur, and splinter hemorrhages may all be clues to the diagnosis of this rare entity in children Postinfectious arthritis is one of the most common causes of acute polyarthritis without fever One to weeks after an illness (especially C trachomatis , Shigella , Salmonella , or Group A Streptococcus ) or urogenital infection (Reiter syndrome), a child may develop an asymmetric joint inflammation predominantly involving large joints of the lower extremities The severity of the antecedent illness has little correlation with the arthritis As with many of the diseases discussed to this point, SLE has a variable clinical presentation with regard to musculoskeletal involvement In fact, no two patients have an identical pattern of immune complex formation or clinical disease expression A symmetric polyarthritis involving peripheral joints of the hands or feet may be seen However, small effusions of the knee are also common with active disease, and the arthritis may also be intermittent or migratory Patients with this type of arthritis are usually afebrile, yet high fever may be a prominent finding Further, although arthritis is one of several diagnostic criteria, it is uncommon for patients with SLE to present with isolated arthritis Arthritis of the small joints, a positive test for ANA, and abnormalities of the skin, kidneys, lungs, or central nervous system should raise the clinician’s suspicion for SLE HSP is rarely a diagnostic challenge thanks to the presence of petechiae and purpura in the characteristic below-the-waist distribution Affected children may