Symptom patterns before and after indolent systemic mastocytosis: A matched cohort analysis.

Background: Systemic mastocytosis (SM) is a clonal mast cell disorder driven in most cases by Objective: We sought to longitudinally describe various aspects of the real-world patient journey in the year leading up to and the year following diagnosis of SM. Methods: This retrospective, observational study included a previously confirmed cohort of patients with SM within a large integrated health system. We assessed physician-coded diagnoses, dispensing of medications, and patient-reported symptoms during the year before and after diagnosis, supplementing manual review with natural language processing outputs to enhance accuracy of symptom identification. Findings were compared with 2 matched comparison groups: patients with chronic spontaneous urticaria (CSU) and patients without SM or CSU. Results: Among 75 patients with SM (59 nonadvanced, 16 advanced), CSU patients with CSU, and 150 patients without SM or CSU, SM was associated with higher frequencies of cardiovascular disease, hepatosplenomegaly, osteoporosis, anemia, thrombocytopenia, eosinophilia, and elevated serum tryptase compared with both comparison groups. Gastrointestinal and neuropsychiatric symptoms were consistently more common in patients with SM, often persisting or worsening after diagnosis despite treatment. Advanced SM was distinguished by more pronounced hematologic and gastrointestinal abnormalities, whereas nonadvanced SM exhibited greater prevalence of cutaneous and neuropsychiatric symptoms. Conclusions: Patients with SM often present with heterogeneous, nonspecific symptoms that overlap with several other conditions, contributing to substantial diagnostic delays. Our findings underscore the need for more inclusive diagnostic approaches and improved management strategies that address the full spectrum of patient experience before and after diagnosis.