In the joints of children with HSP, US revealed no fluid collection in the joint space and no evidence of synovitis or intra-articular inflammation, but it did show subcutaneous swelling around the joint. This finding suggested that painful joint swelling in HSP is an indication of painful subcutaneous edema (angioedema), not arthritis. Arthralgia in patients with HSP is probably caused by swelling and edema of subcutaneous tissues around joints. The prognosis of children with HSP-related arthritis is therefore good because the arthritis is nondeforming and, in our patients, healed spontaneously or with steroids,1–3 in comparison with septic arthritis or synovitis, which necessitate treatments and last longer.
Because of this good prognosis, no studies of imaging findings in arthralgia or arthritis in HSP have been conducted. However, the frequency of arthralgia or arthritis in patients with HSP has been studied clinicially. Accompanying arthralgia or arthritis was reported up to 91.9% of patients with HSP in Turkey.7 In Korea, younger children are more at risk of developing arthritis, according to a nationwide population-based study,3 and affected children younger than 7 years had frequent joint symptoms.2 Our results also demonstrated that the rate of arthralgia was highest among children aged 2–5 years (51.6%) and decreased with age (32.3% of patients aged 6–10 years and 16.1% of those aged 11–17 years).
Periarticular swelling, tenderness, and pain are prominent in HSP-related arthralgia and arthritis, but erythema and joint effusion are rare.1 In our study, erythema (80.6%), swelling (71.0%), and tenderness (67.7%) were common. The high frequency of joint erythema might be related to extensive and multiple areas of purpura around joints. In septic arthritis and synovitis, which are also common in children younger than 5 years, erythema, swelling, and tenderness are observed,12,13 but arthralgia with joint swelling is not. Purpura on the lower legs is evidence of HSP. Therefore, thorough physical examination is helpful in the diagnosis of arthralgia in patients with HSP.
Among patients with HSP, the risk of developing arthritis was reported to be highest in children up to 7 years of age,2 as in our study. A pronounced gender predominance for HSP occurrence was not reported in other studies,1,2,7 whereas in our study, arthralgia was slightly more predominant among boys.
Joint involvement in HSP is usually oligoarticular, and large joints of the lower extremities (knee, ankle, and hip) are most commonly affected.1 According to our results, 75% of the involved joints were ankles and knees.
Subcutaneous edema is the other prominent sign of HSP, with an overall frequency of 38.8–51.3%.7,8,16,17 It an indication for corticosteroid therapy in patients with HSP.1 In previous studies, the majority of subcutaneous edema was located in the extremities, followed by the head and neck8 and back.18 In a study of 163 Turkish children with HSP and subcutaneous edema, the majority (143 [87.7%]) had subcutaneous edema in the extremities, 33 (20.2%) had periorbital or scalp edema, and only 8 (4.9%) of them had scrotal involvement.8 Skin biopsies of subcutaneous edema were performed in 18 patients with HSP but without purpura to confirm the clinical diagnosis. All biopsy specimens showed leukocytoclastic vasculitis, with immunoglobulin A deposits in two and C3 deposits in one.19
Joint involvement and subcutaneous edema in the extremities were less frequent in patients with severe gastrointestinal involvement. Karadağ et al. speculated that arthralgia and subcutaneous edema could be negative predictive factors for severe gastrointestinal involvement in patients with HSP.8 In our study, abdominal pain was present in 9 patients with arthralgia. One of them had hematochezia and endoscopy revealed severe duodenal ulcer before arthralgia appeared.
Prednisone decreased both the prevalence of purpura during the first month after onset and the patient-reported severity and duration of joint pain.20,21 In one study, children with HSP-related arthritis received steroid therapy more frequently than those without HSP-related arthritis (77.4% vs. 56.5%, P < 0.001).2 In our study, steroids for managing the arthralgia were administered in 80.6% of patients. In the other patients, arthralgia spontaneously resolved with supportive care. Recurrences often differ to some extent from the initial episode, in that arthritis is less common with relapses.6 In our study, recurrence was observed in 3 patients during the study period, and 1 had recurrent arthralgia.
This study had some limitations: It was conducted in a single center, the study period was short, and only US findings were reviewed; the pathogenesis was not investigated. Pain in joints might have been related to subcutaneous swelling around the joint. It is not known why the immunoglobulin A immune complex was deposited in the blood vessels around the joint in a previous study; it may be related to the slow blood flow in the small vessels around the joints in children.