Pediatric Case of Calcineurin Inhibitor-Induced Pain Syndrome Diagnosed During Cyclosporine Therapy for Aplastic Anemia

A 15-year-old male with severe aplastic anemia was started on immunosuppressive therapy (IST) comprising antithymocyte globulin and cyclosporine (CsA), along with methylprednisolone and eltrombopag. Eight weeks after starting treatment, the CsA trough level increased to 269 ng/mL, coinciding with bilateral leg pain unresponsive to all analgesics, including fentanyl. MRI revealed diffuse high signal intensity areas on short tau inversion recovery (STIR) sequences in both thigh muscles. After discontinuing CsA and starting nifedipine, the pain improved, and an MRI taken 10 days post-discontinuation showed that the STIR high signal areas disappeared. Re-administration of CsA resulted in a recurrence of pain. Based on the clinical presentation and progression, the patient was diagnosed with calcineurin inhibitor-induced pain syndrome (CIPS). After switching from CsA to tacrolimus, the patient had no recurrence of pain. Although reports of CIPS in pediatric patients are extremely rare, it is important to consider CIPS as a differential diagnosis when a patient taking calcineurin inhibitors presents with severe pain in the lower limbs.