Objective Sleep Assessment in Systemic Mastocytosis: Polysomnographic Findings from a Single-Center Observational Study

Background/Objectives: Systemic mastocytosis (SM) is a rare clonal mast cell disorder associated with mediator-related symptoms and a broad range of neurocognitive and sleep-related complaints. Fatigue, insomnia, and brain fog are frequently reported in clinical practice, but objective polysomnographic data in this patient population remain limited. As overweight and obesity are established contributors to sleep-disordered breathing, polysomnography (PSG) findings in patients with SM should be interpreted with caution when a control group is not available. This study aimed to characterize sleep architecture, sleep continuity, and sleep-disordered breathing in adult patients with SM who underwent PSG. Methods: This single-center observational study included nine adult patients diagnosed with SM from the Ege University Mastocytosis Database between January 2023 and January 2024. No control group was included. All patients underwent overnight laboratory PSG after discontinuation of antihistamine therapy for at least seven days. Demographic characteristics, SM subtype, baseline serum tryptase levels, Epworth Sleepiness Scale (ESS) scores, and brain fog-like cognitive complaints were recorded. PSG parameters included total sleep time, sleep efficiency, sleep onset latency, wake after sleep onset, rapid eye movement (REM) latency, sleep stage distribution, arousal burden, apnea–hypopnea index (AHI), oxygenation parameters, and periodic limb movements. Results: The study included four women and five men, with a median age of 50 years. Eight patients had a body mass index (BMI) ≥ 25 kg/m2, indicating that the cohort was predominantly overweight or obese. The most common SM subtype was indolent SM. The median baseline serum tryptase level was 55.9 ng/mL, and the median ESS score was 9. Only two patients had excessive daytime sleepiness according to ESS > 10, whereas six patients reported brain fog-like complaints. Median sleep efficiency was 91.4%, total sleep time was 344 min, sleep onset latency was 9 min, and wake after sleep onset was 11 min. Median REM latency was 128.5 min. Sleep stage distribution showed median N1, N2, N3, and REM sleep proportions of 3%, 54%, 26%, and 16.7%, respectively. One patient had no observed REM sleep, and two patients had no measurable N3 sleep. The median number of arousals was 55. The median AHI was 8.2 events/hour. Although eight of nine patients met PSG criteria for obstructive sleep apnea (OSA), including five with mild and three with severe disease, this finding should be interpreted in the context of the high prevalence of overweight/obesity in the cohort. All patients with BMI ≥ 25 kg/m2 had OSA, whereas the only normal-weight patient did not. Conclusions: In this single- center observational study, PSG demonstrated frequent sleep-disordered breathing, REM-related changes, and variable arousal burden in patients with SM; however, these findings cannot be separated from the predominance of overweight/obesity and the absence of a control group. Brain fog-like complaints were common, although excessive daytime sleepiness was present in only a minority of patients. Because most patients were overweight or obese and no control group was included, these findings cannot be attributed directly to SM. However, the results suggest that objective sleep assessment may be useful in selected patients with SM, particularly when fatigue, non-restorative sleep, or cognitive complaints are present. Larger controlled studies with BMI-matched groups are needed to clarify the relationship between SM, mast cell mediator activity, and sleep abnormalities.