Management of Mast Cell Activation Syndrome (MCAS)

Prevention Strategies

The American Academy of Allergy, Asthma, and Immunology recommends identifying and avoiding known triggers including insect venoms, temperature extremes, mechanical irritation, alcohol, and certain medications (e.g., aspirin, radiocontrast agents, and specific anesthetic agents) 2
For patients with insect venom sensitivity and history of systemic anaphylaxis, lifelong venom immunotherapy is recommended 2
Nonsedating H1 antihistamines (e.g., fexofenadine, cetirizine) are generally preferred and can be increased to 2-4 times the standard dose for symptom control 1, 3
H2-receptor antihistamines are recommended as first-line therapy for gastrointestinal symptoms and to help H1 antihistamines attenuate cardiovascular symptoms 1
Oral cromolyn sodium is FDA-approved for mastocytosis to reduce abdominal bloating, diarrhea, and cramps; benefits may extend to neuropsychiatric manifestations 1, 3
Leukotriene modifiers (e.g., montelukast or zileuton) may reduce bronchospasm or gastrointestinal symptoms, particularly in patients with increased urinary LTE4 levels 1, 3

The American Academy of Allergy, Asthma, and Immunology recommends that patients with a history of systemic anaphylaxis or airway angioedema be prescribed an epinephrine autoinjector and instructed on proper use 1, 2
Patients with recurrent hypotensive episodes should be trained to assume a supine position immediately 1
Albuterol can be inhaled via nebulizer or metered-dose inhaler to treat bronchospasm 1
If epinephrine is used, the patient should be transported to the emergency department while remaining in the supine position 2

H2-receptor antihistamines are first-line therapy for gastrointestinal symptoms 1
Oral cromolyn sodium can reduce abdominal bloating, diarrhea, and cramps 1
Leukotriene modifiers may help with gastrointestinal symptoms 1, 3
H1-receptor antihistamines are recommended for dermatologic manifestations like flushing, pruritus, urticaria 3
Topical treatments may include water-soluble sodium cromolyn cream for urticaria and pruritus 4
Topical corticosteroids are recommended for skin inflammation 4
Cromolyn sodium benefits may extend to neuropsychiatric manifestations 1
Doxepin may reduce central nervous system manifestations 1

Multidisciplinary management involving surgical, anesthesia, and perioperative medical teams is recommended for perioperative management 4, 5
Pre-anesthetic treatment with anxiolytics (benzodiazepines), antihistamines (H1 and H2 blockers), and possibly corticosteroids is recommended 4, 5
Safer anesthetic agents include propofol, sevoflurane, isoflurane, fentanyl, remifentanil, lidocaine, and bupivacaine 4, 5
Avoid muscle relaxants atracurium and mivacurium (rocuronium and vecuronium may be safer) and succinylcholine 4, 5
Multidisciplinary approach including high-risk obstetrics, anesthesia, and allergy specialists is recommended for pregnancy management 5
Focus on trigger avoidance, prophylactic antihistamines, as-needed corticosteroids, and epinephrine for anaphylaxis is recommended for pregnancy management 5

Treatment should be guided by symptoms and elevated mast cell mediator levels 6
If a patient has increased urinary LTE4 levels, leukotriene antagonists are recommended; if urinary prostaglandin metabolite levels are increased, aspirin might help 7
Some patients with clonal MCAS can progress to systemic mastocytosis, though data from the Mayo Clinic cohort followed for more than 15 years showed no progression to mastocytosis 6
Patients with indolent systemic mastocytosis generally have a normal life expectancy 6

Sedating H1 antihistamines can cause drowsiness, impair driving ability, and lead to cognitive decline, particularly in elderly patients 1, 3
Aspirin should be used with caution and is contraindicated in those with allergic reactions to NSAIDs 1
Long-term steroid use should be avoided due to side effects 1
Eliminating additives in drugs by compounding is not recommended based on evidence from studies in chronic urticaria 2