Mast cell activation syndrome (MCAS) is characterized by recurrent multisystem symptoms
related to inappropriate mast cell mediator release, such as flushing, urticaria, diarrhea, and
throat tightness. Diagnostic criteria traditionally require: (1) symptoms in at least two organ
systems, (2) laboratory evidence of elevated mast cell derived mediators, and (3) symptom
improvement with therapy targeting mast cells such as antihistamines. However, emerging
frameworks such as consensus-2 suggest diagnosis without biomarker elevation if clinical
presentation and therapeutic response are consistent with MCAS.
We present a 55-year-old male with Hashimoto’s thyroiditis, mild intermittent asthma, obstructive sleep apnea, and multiple anaphylactic allergies presenting with a nine year history of flushing, urticaria, fatigue, diarrhea, and throat tightness triggered by various allergens, notably sulfite-containing foods and medications. Physical examination was significant for nasal turbinate erythema during asymptomatic periods and flushing with urticaria during flares. Laboratory evaluation revealed normal tryptase and urinary N-methylhistamine levels, mild eosinophilia, and negative KIT D816V mutation. Despite lacking biomarker evidence, his symptom pattern involved multiple systems and improved with cromolyn sodium and cetirizine, meeting consensus-2 diagnostic criteria.
This case illustrates the diagnostic challenge posed by MCAS in the absence of mediator elevation, particularly given the difficulty of testing during acute flares. While consensus-2 criteria may broaden recognition of MCAS, there is risk of overdiagnosis as many patients present with nonspecific symptoms. Clinicians must balance adherence to established guidelines with careful application of emerging frameworks, using therapeutic response as an adjunctive diagnostic tool to reduce morbidity in complex cases.
We present a 55-year-old male with Hashimoto’s thyroiditis, mild intermittent asthma, obstructive sleep apnea, and multiple anaphylactic allergies presenting with a nine year history of flushing, urticaria, fatigue, diarrhea, and throat tightness triggered by various allergens, notably sulfite-containing foods and medications. Physical examination was significant for nasal turbinate erythema during asymptomatic periods and flushing with urticaria during flares. Laboratory evaluation revealed normal tryptase and urinary N-methylhistamine levels, mild eosinophilia, and negative KIT D816V mutation. Despite lacking biomarker evidence, his symptom pattern involved multiple systems and improved with cromolyn sodium and cetirizine, meeting consensus-2 diagnostic criteria.
This case illustrates the diagnostic challenge posed by MCAS in the absence of mediator elevation, particularly given the difficulty of testing during acute flares. While consensus-2 criteria may broaden recognition of MCAS, there is risk of overdiagnosis as many patients present with nonspecific symptoms. Clinicians must balance adherence to established guidelines with careful application of emerging frameworks, using therapeutic response as an adjunctive diagnostic tool to reduce morbidity in complex cases.