6-Mercaptopurine-associated Sinusoidal Obstructive Syndrome During Interim Maintenance I: A Case Report.

Thiopurine-methyltransferase (TPMT) and nudix-hydrolase-15 (NUDT15) are enzymes relevant to the metabolism of thiopurine medications, used to treat immunologic disorders and malignancies. Standard dosing administered in the setting of TPMT/NUDT15 dysfunction can cause excessive cytotoxic metabolites and life-threatening complications. We describe an adolescent with high-risk B-cell acute lymphoblastic leukemia (ALL) whose TPMT/NUDT15 status was unknown due to lack of insurance approval for genetic testing. He subsequently developed myelosuppression and severe veno-occlusive disease (VOD) after receiving 6-mercaptopurine (6-MP). Our patient provides an example of a very rare 6-MP-related toxicity and the potential benefit of TPMT/NUDT15 screening before initiating thiopurine therapy.

A Unique Presentation of Multicentric Myofibromatosis in the Masseter Muscle of a Pediatric Patient.

A 12-year-old female with a history of multicentric infantile myofibromatosis (IM) presented with a tender, enlarging cheek mass and trismus. Imaging identified an intramasseteric tumor. Given the unknown etiology of the tumor and her bothersome symptoms, the mass was excised using a transoral approach with concurrent facial nerve monitoring. Her pathology report confirmed the diagnosis of a myofibromatosis lesion embedded within the masseter muscle. While IM can often present with lesions in the head and neck region, the intramasseteric location is rare and presents unique considerations for surgical approach. Myofibromatosis lesions typically occur before two years of age, although there are some rare documented cases of multicentric myofibromatosis lesions presenting at older ages. Furthermore, this patient's family history of similar lesions suggests a familial variant, which may have implications for disease behavior and need for further work-up, monitoring, and management. Overall, this was an unusual presentation of IM given the patient's age, prevalent family history, and the location of the mass. This case report adds to the literature and discusses the clinical differential of a pediatric cheek mass, the surgical considerations for an intramasseteric tumor, and the natural history of infantile myofibromatosis.