Macrophage activation syndrome (MAS) is a life-threatening complication in children with rheumatic diseases, particularly systemic-onset juvenile chronic arthritis (SOJCA). Because of the potential fatality of this condition, prompt recognition and immediate therapeutic intervention are important. This study assessed the clinical features of nine MAS events in five children with SOJCA. Nonremitting fever and decreased platelet and white blood cell counts led to a diagnosis of MAS. The urinary β2-microglobulin (β2MG) level was a sensitive indicator of MAS. Serum levels of β2MG and soluble interleukin-2 receptor were also elevated. These biologic markers reflecting hyperactivated cellular immunity are useful indicators of MAS. Four children treated with cyclosporin A (CSP) achieved rapid and complete recovery, but one patient without CSP died due to rapidly progressive respiratory failure. All children treated with CSP responded quickly, and fever abated within 36 h of initiation of treatment. CSP should be added to first-line therapy of MAS.

Although Mp-HLH is a rare complication of M. pneumoniae infection, it should always be considered in patients with antibiotic-refractory M. pneumoniae infections with cytopenia. Mp-HLH might be effectively treated by corticosteroids or high-dose gammaglobulin. To clarify the diverse clinical manifestations of M. pneumoniae infections, immunological interactions between M. pneumoniae and the host immune system should be further investigated.

The prevalence of H. pylori infection in children with cITP is not high. However, the platelet count increased after eradication therapy in a boy with cITP. It is suggested that the eradication of H. pylori infection would be valuable in children, as well as in adults, with cITP.

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Primary anaplastic large cell lymphoma (ALCL) of skeletal muscle is very rare. We report a case of ALCL arising from the left psoas muscle. A 14-year-old girl presented with a large left inguinal tumor. She complained of a 2-month history of left leg pain, which had been exacerbated upon leg extension, and she had become aware of a rapidly growing left inguinal tumor 3 weeks before admission. CT scan and MRI revealed a large tumor arising from the left major psoas muscle and protruding into the inguinal region. In view of the tumor’s location and the patient’s age, soft tissue tumors such as rhabdomyosarcoma and primitive neuroectodermal tumor were initially considered. However, histopathological examination yielded a diagnosis of anaplastic lymphoma kinase-positive ALCL. The serum level of soluble interleukin-2 receptor was markedly elevated at 50,414 U/ml, and this also strongly suggested ALCL. Although rarely reported, ALCL is an important entity to consider in the differential diagnosis of skeletal muscle tumors in children and young adults.