I suspect MCAS

Mast Cell Activation Syndrome (MCAS) can be difficult to recognise because symptoms affect multiple body systems, typically fluctuate over time and overlap with many other conditions. Patients may have seen several specialties or received multiple diagnoses before Mast Cell Activation Syndrome is considered as a possible explanation for their wider pattern of symptoms.

When should I consider MCAS?

You may wish to consider MCAS where a patient presents with symptoms affecting multiple body systems, particularly where there is a relapsing–remitting pattern or symptoms occur across different systems at the same time.

These may include:

• Skin: flushing, hives, itching and/or angioedema
• Gastrointestinal: abdominal pain, bloating, reflux, diarrhoea, constipation and/or nausea
• Respiratory: wheeze, throat tightness and/or breathlessness
• Cardiovascular: palpitations, fainting and/or chest pain
• Neurological: headaches, brain fog and/or fatigue
• Genitourinary: bladder, vulval and/or prostate symptoms
• Gynaecological: heavy and/or painful periods
• Musculoskeletal: joint and/or muscle pain

Other clues in the clinical history

Patients with suspected MCAS may also have:

• Allergy-type reactions, including flushing, urticaria, throat closing, and/or anaphylaxis, which are not adequately explained by conventional allergy testing
• Reactions to foods, medications or medication excipients
• Sensitivity to environmental triggers such as fragrances, temperature changes or stress
• Reactions which are trigger-dependent but can appear inconsistent
• Symptoms which fluctuate considerably in type and severity
• Several existing diagnoses affecting different body systems
• Extensive healthcare contact without a clear unifying diagnosis
• A family history of similar patterns of symptoms
• Non-specific or medically unexplained symptoms, such as fatigue, chronic pain, headaches, abdominal symptoms, or anxiety, particularly where routine investigations are normal or inconclusive
• A relapsing–remitting pattern of illness, often without an obvious unifying diagnosis

No individual symptom or feature confirms MCAS. Many of these presentations have other possible causes, and appropriate investigation and consideration of differential diagnoses remain important.

What should I do next?

If the clinical picture raises the possibility of MCAS, our Primary Care Guide to MCAS provides practical information for healthcare professionals on recognising the presentation, taking an appropriate clinical history, investigations, differential diagnoses and management.

You can also explore the other sections of our website for more information about diagnosing MCAS, testing and investigations, treatment and referral. You may find our information on symptoms and diagnosing MCAS particularly useful.

For further learning, explore our YouTube channel for more educational content and expert discussions and check out our podcast - 'Let's Talk MCAS' where we speak with clinicians, researchers and members of the MCAS community. 

Investigating MCAS

If you are considering Mast Cell Activation Syndrome (MCAS) as a possible diagnosis for a patient, our resources can support you through the investigation process.

Explore information on diagnostic criteria, appropriate testing and interpreting results, alongside practical guidance to support management.