Severe Anemia With Intraosseous-Intramuscular Hemorrhage in a Patient With Kit-C-Negative Systemic Mastocytosis.

Systemic mastocytosis (SM) is a rare hematologic disorder characterized by clonal proliferation of mast cells in various tissues, often presenting with skin lesions, gastrointestinal symptoms, or anaphylaxis. However, atypical presentations lacking these classical features may delay diagnosis and complicate management. We report the case of a 42-year-old woman who presented with progressive anemia, recurrent spontaneous intramuscular and intraosseous hemorrhages, and severe, unexplained pain. Notably, she lacked cutaneous signs or known allergic triggers. Extensive laboratory and imaging workups ruled out common hematologic and autoimmune causes. Bone marrow biopsy ultimately revealed multifocal clusters of atypical mast cells consistent with SM, despite the absence of the KIT D816V mutation. This case underscores the protean manifestations of SM and the need to maintain a high index of suspicion in patients with unexplained cytopenia and bleeding. It also highlights the role of bone marrow evaluation in the diagnostic pathway, even when classic clinical features are absent. Timely recognition of atypical SM can guide appropriate management and improve patient outcomes.