Transient synovitis, also known as toxic synovitis, is the most common cause of hip pain in childhood. It is a self-limited condition caused by a nonpyogenic inflammatory response of the synovium. Its peak incidence is between 3 and 6 years of age and it affects boys more commonly than girls, with a slight predilection for the right hip. Less than 5% of cases are bilateral. Pain may be referred to the medial aspect of the thigh or knee. An association with active or recent infection, trauma, or allergic hypersensitivity is suspected. Many children with transient synovitis have or recently have had an upper respiratory illness.

Affected patients either refuse to walk or walk with a limp. The leg is held in flexion with slight abduction and external rotation. Passive movement is usually pain-free; however, there may be pain and a slightly decreased range of motion with extreme internal rotation or abduction. Low-grade fever and malaise may be present. The diagnosis of transient synovitis is one of exclusion, as laboratory values may be normal or may reveal mild elevations in the white blood cell (WBC) count and erythrocyte sedimentation rate (ESR). Clinical decision rules have been developed to help differentiate transient synovitis from septic arthritis based on the presence or absence of fever, the ability to bear weight, WBC counts, and inflammatory markers (ESR and C-reactive protein [CRP]) (Chapter 109). In the absence of fever and without elevated WBC and ESR, septic joint is unlikely, and the diagnosis of transient synovitis can be made without obtaining joint fluid. Kingella kingae septic arthritis, however, can present with minimal clinical abnormalities and may be mistaken for transient synovitis,¹ so it is imperative that you provide these patients with close follow-up. Anteroposterior (AP) and “frog-leg” lateral radiographs of the pelvis tend to be normal in transient synovitis; other findings consistent with transient synovitis include medial joint space widening, an accentuated pericapsular shadow, and Waldenström sign, which is lateral displacement of the femoral epiphysis with surface flattening secondary to effusion. These findings are also apparent in Legg–Calvé–Perthes (LCP) disease and, if present, mandate close follow-up or further investigation with MRI. Although effusions are present in 60% to 70% of cases of transient synovitis, they are also present in septic arthritis, osteomyelitis, acute slipped capital femoral epiphysis (SCFE), LCP disease, rheumatoid and infectious arthritis, malignancy, and osteoid osteoma, thereby limiting the utility of an effusion on ultrasonography in determining the etiology of hip pain.

Treat with rest and anti-inflammatory medications to reduce the synovitis.² Allow children a gradual return to activity as the pain subsides and full, unrestricted activity when the hip is completely pain-free and the limp has resolved. Ensure a repeat examination within 12 to 24 hours and again after 10 to 14 days if the symptoms have not resolved. Up to 75% of patients have complete resolution of pain within 2 weeks and 88% within 4 weeks. The remainder may have less intense, but persistent pain for up to 8 weeks. Relapse is infrequent, and usually occurs within 6 months.

SLE is a chronic but often episodic multisystem autoimmune disease with protean manifestations. Fifteen to twenty percent of patients develop symptoms before 18 years of age.³ SLE is rare in those younger than 5 years.⁴ Children often present with nonspecific symptoms resulting in a delayed diagnosis. Juvenile SLE is more aggressive than adult SLE with a higher prevalence and severity of renal and central nervous system (CNS) disease. Female patients are preferentially affected. Native Americans, Hispanics, Chinese, and Filipinos are more susceptible to developing SLE, and greater disease severity is seen in African Americans and Hispanics. Patients with lupus are more likely to have a relative either with lupus or another autoimmune disease such as thyroiditis or insulin-dependent diabetes.

The most common presenting findings of pediatric SLE (pSLE) include hematologic (anemia, lymphopenia, leukopenia, and/or thrombocytopenia), mucocutaneous (malar rash and/or oral ulcers) (Fig. 111-1), musculoskeletal (arthritis or arthralgia), fever, and renal abnormalities. Sun exposure can exacerbate the skin disease and cause a systemic flare.

Most patients will have musculoskeletal involvement such as arthritis, arthralgia, myalgia, diffuse muscle weakness, tenosynovitis, periostitis, and, less commonly, myositis. The arthritis of pSLE tends to be nonerosive and nondeforming. It is painful, symmetric, and polyarticular and can affect small or large joints; prolonged morning stiffness is also common. Avascular necrosis (AVN) is a well-recognized complication of pSLE affecting 5% to 40% of patients.⁵ AVN most commonly affects the hips and knees and may be due to the illness, complications of the illness (i.e., nephritis) or as a consequence of steroid therapy.^6,7 Osteoporosis and vertebral fractures can also occur.

Approximately 75% of children with pSLE will have renal involvement, usually within 2 years of disease onset. Renal disease is the leading cause of serious morbidity and mortality in SLE. Early findings include microscopic hematuria and proteinuria; hypertension, decreased glomerular filtration rate, azotemia, and renal failure may develop. Lupus nephritis classification is based on histopathology and can range from normal by light microscopy (class I) to advanced sclerotic nephritis (class VI). As treatment differs for differing forms of SLE nephritis, renal biopsy is warranted. Renal flares are common and can frequently be detected by worsening proteinuria before the development of constitutional symptoms (fever, malaise, anorexia, and weight loss).

CNS disease is the second leading cause of serious morbidity and mortality in SLE and is difficult to diagnose because of vague and varied complaints. Headache is the most common neuropsychiatric manifestation. Severe unremitting headache may reflect vasculitis, cerebral vein thrombosis (CVT), CNS infection, pseudotumor cerebri, or organic brain syndrome. CVT may present without other CNS manifestations and is almost always associated with the presence of lupus anticoagulant. Other neuropsychiatric manifestations of pSLE include psychosis, altered mental status, cognitive dysfunction, cerebrovascular disease, seizures, movement disorders, neuropathy, and transverse myelitis.

Hematologic abnormalities include anemia, which may be from hemolysis but most commonly reflects the presence of chronic disease. Thrombocytopenia can occur, as can leukopenia. Involvement of serosal membranes can result in pleuritis with or without pleural effusion, peritonitis, and pericarditis. Pericarditis can occasionally result in a clinically significant pericardial effusion. Cardiac complications include myocarditis, endocarditis, and premature atherosclerosis causing coronary artery disease. Pulmonary disease includes pneumonitis, and infrequently, pulmonary hemorrhage or pulmonary hypertension. Shrinking lung syndrome may also occur and results from diaphragmatic dysfunction that elevates the lung, resulting in decreased lung volume. Gastrointestinal (GI) disease is uncommon in pSLE but may include pancreatitis, mesenteric vasculitis, and hepatitis.

Although it is unlikely that the initial diagnosis will be made in the emergency department (ED), it is important to exclude malignancies, especially leukemia, ARF, JIA, and infectious processes. Drug-induced lupus is seen in children as well as adults. The medications most commonly implicated are anticonvulsants (phenytoin and carbamazepine), isoniazid, and minocycline.⁵ If a patient with SLE symptoms is taking these medications, discontinue their use immediately.

In all patients with suspected SLE, obtain a complete blood count, prothrombin time (PT), international normalized ratio (INR), partial thromboplastin time (PTT), serum electrolytes, blood urea nitrogen, creatinine, ESR, and CRP. Urinalysis will often reveal microscopic hematuria and proteinuria. If there is evidence of coagulopathy, lupus anticoagulant and antiphospholipid antibody tests are indicated. Obtain antinuclear antibody (ANA), other autoantibodies, rheumatoid factor, complement studies, and quantitative immunoglobulins. ANA is positive in almost all patients who have active disease but is not specific (may be positive in up to 33% of healthy patients). Antibodies to double-stranded DNA (anti-ds DNA) are more specific to SLE and are found in 60% to 70% of patients with SLE.

Over the course of the illness, children with SLE develop malar rash, neurologic features (headache, chorea, seizures), and renal disease more frequently than do adults. Hematologic and renal involvement tends to be worse in children. Over the past several years, the overall prognosis of pSLE has improved due to earlier diagnosis and improved treatments. The primary causes of death are renal disease, infection, and CNS disease.

Treatment of SLE includes nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, immunosuppressants, and biologic agents; the choice of medication depends on the extent of organ system involvement.

Acute rheumatic fever (ARF) is an autoimmune systemic inflammatory response to infection with GAβHS. ARF occurs after GAβHS pharyngitis but is not associated with streptococcal skin infections. Worldwide, rheumatic heart disease (RHD), a complication of ARF, is the most common form of acquired heart disease in all age groups.

The incidence of ARF peaks between 5 and 15 years of age. Only 5% of episodes arise in children younger than 5 years and it is almost unheard of in children younger than 2 years old.⁸ ARF is more common in girls. It is most common during the winter and spring. Although ARF generally develops 2 to 4 weeks following the inciting infection, it may present weeks to months later. One-third of children do not recall an antecedent sore throat.

The main clinical features of ARF are outlined in the modified Jones criteria (Table 111-1).⁹ The World Health Organization (WHO) has also developed criteria to aid in diagnosing ARF (Table 111-2). The WHO criteria are less stringent than the revised Jones criteria to reflect the increased incidence of ARF in developing countries. As diagnostic guidelines, they can be adapted to populations at high risk for ARF to improve the sensitivity for disease detection. Chorea and indolent carditis are not diagnosed until months after the onset of ARF, and due to waning or nonexistent antibody titers do not require evidence of an antecedent GAβHS infection.

Joint complaints are common in ARF and range from arthralgias to frank arthritis. Arthralgia is a minor manifestation of ARF in the absence of arthritis. The arthralgias are especially intense at night and can wake children from sleep. Pain is out of proportion to the clinical findings. Arthritis is a major manifestation of ARF and occurs in approximately 75% of cases. Classically, it involves larger joints, especially the knees, ankles, wrists, and elbows, and is migratory. Monoarticular arthritis is less common but may occur, especially with early use of anti-inflammatory medications. Synovial fluid in ARF usually has 10,000 to 100,000 WBC/mm³ with a predominance of neutrophils, protein of ≥4 g/dL, normal glucose, and the ability to form a good mucin clot. ARF arthritis responds dramatically to salicylates. There tends to be an inverse relationship between the severity of the arthritis and the severity of carditis. Joint symptoms of ARF tend to resolve within a month and leave no permanent damage.