What are red flags for neoplasia as the etiology of joint pain?
- • Joint redness.
- • Fever, weight loss, night sweats.
- • Night time pain.
- • Adenopathy.
- • Associated bone pain (i.e., pain between joints and on direct palpation) out of proportion to physical findings.
Malignancy must be considered in any child in whom a diagnosis of systemic JIA is entertained since the classic features of systemic JIA (i.e., fever, rash, and arthritis) are also seen in malignancy. Malignant infiltration of bone or synovium may mimic polyarthritis. In addition, joint effusions occur in children with malignancy, possibly owing to antigen–antibody complex deposition producing a serum sickness-like picture. This may also be responsible for the tremendous inflammatory response (high erythrocyte sedimentation rate [ESR] and anemia) seen in some children with malignancy, again mimicking systemic JIA.
Acute leukemia causing polyarthritis should be suspected in children with an elevated ESR but low platelet counts . Other frequent laboratory abnormalities are an elevated LDH (>2x upper limit of normal), elevated uric acid, and abnormal peripheral blood smear. Notably, the white blood cell (WBC) count and differential may initially be normal. Blasts on blood smear may be a later finding.
Radiographs of affected joints and/or whole body bone scans may be helpful in diagnosis. Bone marrow examination is recommended prior to initiation of high-dose corticosteroid therapy for systemic JIA in cases where the diagnosis is unclear, since inappropriate use of corticosteroids in malignancy can worsen prognosis.