The correct answer is:

Henoch–Schönlein purpura (HSP)

Educational Objective:

Recognize the manifestations of Henoch–Schönlein purpura (HSP).

Key Point:

HSP is a small-vessel vasculitis with symptoms that can include purpura and ecchymoses of the legs or buttocks, as well as abdominal pain, intussusception, gastrointestinal bleeding, and joint pain and effusions.

Explanation:

Henoch–Schönlein purpura (HSP) is a common, small-vessel pediatric vasculitis, and its symptoms are related to the areas of injury to the small vessels. Oftentimes, HSP follows an upper respiratory illness, but the cause is typically unknown.

HSP usually appears as palpable purpura that develops into petechiae or ecchymoses on the legs or buttocks. Renal, musculoskeletal, and gastrointestinal involvement may also be present, as well as arthritis, abdominal pain, intussusception, hematuria, proteinuria, nephritis, and, in some cases, renal failure.

No laboratory study is diagnostic, but there may be leukocytosis, thrombocytosis, and mild anemia. Due to the inflammation and vasculitis, an elevated erythrocyte sedimentation rate (ESR) will be present. Treatment is supportive, although steroids are sometimes added.

Hemolytic uremic syndrome (HUS) is characterized by a low platelet count, renal injury, and microangiopathic hemolytic anemia. Urine dipstick analysis normally shows hematuria and proteinuria. HUS caused by exotoxin-producing Escherichia coli often occurs several days after gastroenteritis with bloody diarrhea. Laboratory values will show a low platelet count and a low hemoglobin level.

Acute rheumatic fever frequently follows a case of group A streptococcal pharyngitis. The Jones criteria were developed to aid in the diagnosis. Possible skin manifestations include erythema marginatum and subcutaneous nodules. ESR and C-reactive protein level may be elevated.

Kawasaki disease is a vasculitis that particularly targets the coronary arteries. The clinical criteria used to diagnose a case of Kawasaki disease include erythema of the hands and soles, a viral exanthem, conjunctival injection, cervical lymphadenopathy, and persistent fever. Laboratory findings may include leukocytosis, anemia, and thrombocytosis.

References:

Ardoin SP, Fels E. Vasculitis syndromes (chapter 167). In: Kliegman R, et al, eds. Nelson Textbook of Pediatrics. 20th ed., 2016:1215-1223.

Ombrello AK, Kastner DL. Hereditary periodic fever syndromes and other systemic autoinflammatory diseases (chapter 163). In: Kliegman RM, et al, eds. Nelson Textbook of Pediatrics. 20th ed., 2016:1193-1204.

Son MB, Newburger J. Kawasaki disease (chapter 166). In: Kliegman RM, et al. Nelson Textbook of Pediatrics. 20th ed., 2016:1209-1214.

Van Why SK, Avner ED. Hemolytic-uremic syndrome (chapter 518). In: Kliegman RM, et al, eds. Nelson Textbook of Pediatrics. 20th ed., 2016:2507-2509.