Rheumatic diseases include both primary vascular disorders, as well as disorders of connective tissues. Almost any organ can be affected, from the heart and lungs to the bones, joints or skin, and the clinical presentation can vary greatly, depending on the site involved. Three of the most common rheumatic disorders that can present in childhood are juvenile idiopathic arthritis (JIA, also known as juvenile rheumatoid arthritis), systemic lupus erythematosus (SLE), and juvenile dermatomyositis (JDMS).

Although there can be some overlap between these three diseases, they each have distinct criteria that should be met for accurate diagnosis. In JIA, children younger than 16 years of age must exhibit the presence of arthritis in at least one joint for more than 6 weeks, and other types of childhood arthritis should have been excluded. Common classifications include pauciarticular JIA (involvement of four or fewer joints during the first 6 months of illness), polyarticular JIA (involvement of five or more joints during the first 6 months of illness; may be associated with mild systemic symptoms, such as fever or malaise), and systemic-onset JIA (extra-articular manifestations, such as fever or rash, tend to precede the onset of articular symptoms, and complications, like pericarditis and pleuropericarditis, are more common).

The diagnosis of SLE is made if the clinician can detect the presence of four or more of the 11 criteria as proposed by the American College of Rheumatology. These criteria are as follows: malar rash, discoid rash, photosensitivity, oral ulcers, arthritis, serositis, renal, neurologic, hematologic, or immunologic disorders, and/or the presence of antinuclear antibodies (ANAs).

JDMS can have diagnostic similarities to other rheumatic diseases. Many patients with JDMS can have a characteristic rash that may be confused with the malar rash of SLE. Unlike in SLE, patients with JDMS also present with symmetric proximal muscle pain and/or weakness, involving the shoulder and pelvic girdles, and fatigue.

Blood tests are often used in conjunction with the history and physical to support a particular diagnosis. ANAs, one of the diagnostic criteria of SLE, may be present in any number of rheumatic diseases, as well as nonrheumatic diseases, such as neoplasms or infections. It can also be seen in up to 15% to 30% of the normal population, making it a nonspecific finding. ANA is also used to stratify the risk of certain disease complications; for example, patients with JIA that are ANA-positive are at a greater risk of development uveitis. Anti-double-stranded DNA or anti-Smith antibodies may be present in SLE. Both are less sensitive, but much more specific than ANA for SLE. Rheumatoid factor may be seen in both rheumatic and nonrheumatic diseases, but its presence in JIA can be associated with more severe erosive joint disease and poorer functional outcomes. Children with JDMS often have elevated muscle enzymes (i.e., creatine kinase, aspartate aminotransferase, lactate dehydrogenase, and aldolase), nonspecific markers of muscle inflammation that may be elevated in a number of diseases.