STAT5b gain-of-function disease in a child with mycobacterial osteomyelitis of the skull: rare presentation of an emerging disease entity.

purposeSTAT proteins play a key role in several cellular functions related to cell development, differentiation, proliferation, and survival. Persistent STAT activation due to somatic STAT5b

methodsA 3-year-old male with a known STAT5b gain-of-function mutation presented with a 10-day history of a firm, immobile, non-painful cranial mycobacterium mass with dural infiltration located anterior to the coronal suture. Stepwise management finalized with complete resection of the lesion with calvarial reconstruction. A case-based literature review was performed evaluating all patients with this mutation who developed cranial disease.

resultsThe patient was symptom and lesion-free at 1 year since surgical resection and initiation of triple mycobacterial pharmacotherapy. Our literature review demonstrated the rarity of this disease, as well as other presentations of this disease in other patients.

conclusionPatients with STAT5b gain-of-function mutations have attenuated Th1 responses and are treated with medications, such as JAK inhibitors, which further inhibit other STAT proteins that regulate immunity against rare infectious entities, such as mycobacterium. Our case highlights the importance of considering these rare infections in patients on JAK inhibitors and with STAT protein mutations. Possessing a clear mechanistic understanding of this genetic mutation, its downstream effect, and the consequences of treatment may enhance a physician's diagnostic and clinical management of similar patients in the future.