Patient Reported Symptoms and Tryptase Levels in WHO-Defined Systemic Mastocytosis (SM) Versus Mast Cell Activation Syndrome (MCAS) Versus Neither

Introduction: The utility of patient reported symptoms and serum tryptase levels in distinguishing those with systemic mastocytosis (SM) versus mast cell activation syndrome (MCAS) versus those not meeting formal diagnostic criteria for SM or MCAS has not been systematically examined.

Methods: This study was approved by our institutional review board. Patients were referred for suspected SM based on symptoms of mast cell activation, osteopenia, skin rash, etc., or had an established diagnosis of SM. All patients were given a Mastocytosis Symptom Assessment Form (MastSAF) to complete at their initial evaluation. The MastSAF is comprised of 36 symptom questions to be graded on a scale of 0 (absent) to 10 (worst imaginable), and is organized around 9 symptom clusters: gastrointestinal (8 questions), constitutional (3 questions), musculoskeletal (5 questions), cutaneous (4 questions), neuropsychological (6 questions), genitourinary (3 questions), respiratory (4 questions), angioedema (1 question), and cardiovascular (2 questions). All patients underwent bone marrow biopsy and serum tryptase level assessment. SM was diagnosed by 2008 WHO criteria. In the presence of characteristic symptoms, if clonal or abnormal mast cells were not identified, and if serum/urine mast cell mediator levels were increased, then non-SM associated, non-monoclonal MCAS was diagnosed.

Results: A total 53 patients were studied.

1) SM: Of 28 patients, 13 had indolent SM (ISM), 9 aggressive SM (ASM) and 6 SM with associated hematological disease (SM-AHD)

The median total symptom score was 47 (range 8-159). The median (range) for SM subgroups was: ISM 51 (9-159), ASM 55 (19-157) and SM-AHD 27 (8-131) (p=0.2). The normalized median score for individual symptom categories (total median score/no. of symptoms per category) in order of severity was cutaneous 1.9, gastrointestinal 1.8, constitutional 1.7, neuropsychological 1.3, respiratory 1.3, musculoskeletal 0.9, cardiovascular 0.3, genitourinary 0.3, and angioedema 0. Symptom severity was not significantly different among the 3 SM subgroups, except for constitutional symptoms (median score ASM 9, ISM 4, SM-AHD 2.5, p=0.02).

The median (range) tryptase level was 48.4 ng/mL (8.8-282); four patients (14%) had a baseline level <20 ng/mL. The median (range) tryptase level among SM subgroups was: ISM 46.9 (8.8-225), ASM 103 (29.4-282), and SM-AHD 43.5 (28.5-233) (p=0.1). When considering patients with tryptase level ≥50 versus <50 ng/mL, symptom scores were not significantly higher in the former group with the exception of constitutional (p=0.02) and genitourinary symptoms (p=0.04).

2) MCAS: 15 patients

The median total symptom score was 127 (range 2-248). The normalized median score for individual symptom categories in order of severity was neuropsychological 4.5, musculoskeletal 4.2, cutaneous 4.0, constitutional 3.3, gastrointestinal 2.1, respiratory and cardiovascular 2.0 each, genitourinary 1.7, and angioedema 1.0.

The median (range) serum tryptase level at referral was 12.7 ng/mL (1.7-25.8); five patients (33%) had a baseline level >20 ng/mL.

3) Neither SM/MCAS: 10 patients

The median total symptom score was 119 (range 45-177). The normalized median score for individual symptom categories in order of severity was musculoskeletal 4.2, gastrointestinal 3.6, constitutional 3.3, neuropsychological 3.3, cutaneous 3.0, cardiovascular and genitourinary 2.0 each, respiratory 1.3, and angioedema 0.

The median (range) serum tryptase level at referral (n=9) was 4.8 ng/mL (2.9-6.6).

4) Comparison:

MCAS vs. SM: Symptom scores were significantly higher in MCAS as compared to SM (p<0.05), except for genitourinary and respiratory symptoms, which were not significantly different.

‘Neither SM/MCAS’ vs. SM: Symptom scores (total, gastrointestinal, constitutional, musculoskeletal, cutaneous, and neuropsychological) were significantly higher in the former group (p<0.05). Other symptom scores were not significantly different.

Conclusions: The spectrum and severity of patient reported symptoms was broadly similar among WHO subcategories of SM, and serum tryptase level had limited if any correlation with symptom scores. Despite the significantly higher overall symptom burden in MCAS versus SM, tryptase levels in the former group were significantly lower with values >30 ng/mL unusual. Despite overlap, the top ranked symptoms in the 3 groups were different.