The Platelet Millionaire: A Rare Cause of Thrombocytosis in an Adolescent

Objectives:

• Primary myelofibrosis is rare in pediatrics, often manifesting as persistent idiopathic thrombocytosis.

• Transitions from pediatric to adult medical care can be complicated by workup requiring invasive procedures.

J.M., an 18-year-old healthy male, presented for excessive gingival bleeding after wisdom tooth extraction. Workup revealed persistent thrombocytosis to 1,165K, prompting a referral to hematology-oncology. A peripheral smear was notable for many platelets but normal RBC morphology. He had splenomegaly on abdominal ultrasound and a decreased von-Willebrand's activity to antigen ratio, suggesting acquired vWD. A bone marrow biopsy was advised; however, J.M. became lost to follow up for over 9 months owing to self-reported anxiety about the procedure. He remained asymptomatic in this interim until he re-presented to clinic for easy bruising, with no other evidence of bleeding at the time. The biopsy was pursued, revealing hypercellular marrow for age with left shifted granulocytic and erythroid maturation, abnormal megakaryocytes, and 3% blasts. This was consistent with primary early myelofibrosis (PMF), positive for MF-1, CALR, and TP53 mutations and negative for JAK2 and BCR-ABL. He was transitioned to adult hematology, maintained on baby aspirin, and referred for potential allogeneic hematopoietic stem cell transplant (HSCT).

PMF is characterized by marrow fibrosis due to secretion of fibroblast growth factor by clonally proliferative megakaryocytes. It is a disease of adulthood, with 67 years being the median age at diagnosis. Only 100 cases have been reported in children, most of which are secondary to AML, ALL or other malignancies.¹ Most patients present with complications of extramedullary hematopoiesis or bleeding.² Diagnosis is suggested by a leukoerythroblastic picture on peripheral smear and confirmed with a bone marrow biopsy "dry tap" revealing marrow fibrosis.³ Prognosis in pediatric PMF is difficult to predict but outcomes tend to be worse;⁴ TP53 mutation is rare and based on limited adult studies may portend a poorer prognosis.⁵ Our young patient with this rare mutation was therefore referred for HSCT evaluation. Further complicating this case was J.M.'s anxiety, which delayed definitive diagnosis by biopsy. He only agreed to it when, at the med-peds clinic, the concept of local pain management was discussed. Anticipation of upcoming procedures by primary care physicians and close follow-up is especially important for patients transitioning from pediatric to adult providers.