SUN-802 - Osteoporotic Fracture May Signal Transformation of Cutaneous to Systemic Mastocytosis: A Case Report

Introduction 
The association of systemic mastocytosis (SM) and osteoporosis is well established and should be considered in the differential diagnosis during the evaluation of patients with unexpected fragility fractures with no identifiable causes. Risk of osteoporotic fracture is less than 4% for patients with cutaneous mastocytosis (CM) but up to 43% for patients with SM. Adults with CM are at risk for developing SM. We present a case where a fragility fracture signaled the presence of indolent SM in a patient with a history of CM and long-standing signs and symptoms of SM.

Case report   
 A 49-year-old premenopausal woman presented to endocrinology clinic after sustaining an oblique fracture through the left femoral neck from a ground level fall. A DXA scan showed Z-scores of -1.5 right femoral neck, -1.6 total hip, and +0.2 right radius. Her medical history was significant for autoimmune hypothyroidism, CM, palpitations and cardiac ectopy, recurrent pre-syncopal episodes, and chronic abdominal pain refractory to treatment with proton pump inhibitors. She also has a history of frequent emergency room visits, including once for allergy to Levofloxacin, and another for anaphylaxis and syncope after eating a fish sandwich. Her examination was unremarkable, without tachycardia or skin rash. Laboratory: normal (including CMP, vitamin D and PTH of 59.6 pg/mL) except for elevated Tryptase (17.1 mcg/dL; ref 2.2 – 13.2). Bone marrow biopsy: > 25% atypical mast cells, detection of KIT D816V and co-expression of CD2 and CD25 on mast cells by flow cytometry, meeting criteria for diagnosis of SM.

Discussion and conclusion 
Neoplastic mast-cell derived factors result in increased osteoclastic bone resorptions and impaired osteoblastic function via multiple mechanisms (RANK-L signaling, inflammatory cytokines and microRNA expression). Earlier recognition of seemingly disparate symptoms and conditions in this patient may have led to a timely unifying diagnosis of SM, although there are no accepted strategies for prevention of osteoporosis in patients with SM. Physicians treating adult patients with CM should maintain vigilance for SM and screen with Tryptase level. Our patient was treated with Avapritinib (KIT p.D816V selective tyrosine kinase inhibitor), Omalizumab (anti-IgE monoclonal antibody) and Zoledronic acid for osteoporosis, with repeat DXA significant for improved Z-scores of -0.5 right femoral neck, +0.5 total hip, +2.1 lumbar spine and +0.9 right radius.

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