From the Guidelines
Mast cell activation syndrome (MCAS) is a primary clinical condition in which patients present with spontaneous episodic signs and symptoms of systemic anaphylaxis concurrently affecting at least 2 organ systems and resulting from secreted MC mediators, as defined by the most recent and highest quality study 1.
Definition and Diagnosis
MCAS is characterized by the excessive release of chemical mediators from mast cells, leading to allergy-like symptoms affecting multiple body systems. The diagnosis of MCAS is challenging and based on symptom patterns, response to medications, and sometimes laboratory tests measuring mast cell mediators like tryptase, histamine, or prostaglandins 1.
Symptoms and Treatment
MCAS can manifest as flushing, hives, gastrointestinal issues, respiratory problems, and cardiovascular symptoms like tachycardia or hypotension. Treatment typically involves a combination of H1 antihistamines like cetirizine (10mg daily) or fexofenadine (180mg daily), H2 blockers such as famotidine (20mg twice daily), and mast cell stabilizers like cromolyn sodium (200mg four times daily before meals) 1. For acute reactions, epinephrine auto-injectors should be available. Patients should avoid identified triggers, which commonly include certain foods, medications, temperature extremes, alcohol, and stress. A low-histamine diet often helps manage symptoms.
Key Features and Mediators
A key feature of MCAS is recurrent episodes of systemic anaphylaxis with concurrent involvement of at least 2 of the 4 organ systems. The clinical symptoms have to be associated with an acute increase in specific biologic mediator levels, and patients should respond to therapy with MC mediator blocking agents, MC stabilizers, or both 1. The most validated mediators for their direct clinical effect include histamine, PGD2, and LTC4, with the metabolites of these mediators (along with tryptase) serving as biomarkers for MC activation.
Management and Prognosis
The management of MCAS involves a multidisciplinary approach, including avoidance of triggers, pharmacotherapy, and lifestyle modifications. With proper treatment and management, patients with MCAS can experience significant improvement in their symptoms and quality of life 1. However, the prognosis of MCAS varies depending on the severity of the condition and the effectiveness of treatment.
From the Research
Definition and Characteristics of Mast Cell Activation Syndrome (MCAS)
- Mast Cell Activation Syndrome (MCAS) is a chronic multi-system disorder caused by inappropriate mast cell activation 2
- It is characterized by systemic severe and recurrent mast cell activation, usually in the form of anaphylaxis, and a substantial increase of the serum tryptase level beyond the individual's baseline 3
- MCAS can present with a range of symptoms, including gastrointestinal symptoms, such as irritable bowel syndrome, dyspepsia, chronic or cyclical nausea, and heartburn 2
- It can also present with symptoms involving the dermis, cardiovascular system, and neurologic complaints 4
Diagnosis and Diagnostic Criteria
- The diagnosis of MCAS can be made based on medical history and measurable biomarkers 2
- Proposed diagnostic criteria for MCAS include signs and symptoms involving the dermis, gastrointestinal tract, and cardiovascular system, frequently accompanied by neurologic complaints 4
- Diagnostic criteria may also include a response to drugs directed against mast cells, mast cell-derived mediators, or mediator effects 3
- Differential diagnosis is important to separate MCAS from other conditions with overlapping symptoms, such as mastocytosis, atopic diathesis, and overt IgE-dependent and IgE-independent allergies 5
Treatment and Management
- Treatment of MCAS is directed at modulating mast cell activation and the effects of the mediators 2
- Simple over-the-counter medications, such as H1-antihistamines, may be effective in managing symptoms of MCAS 6
- A personalized treatment approach is necessary, taking into account accompanying underlying and potentially complicating conditions, and comorbidities 3
- Multidisciplinary investigations may be required to establish an optimal management plan and provide an optimal quality of life and low risk of anaphylaxis 3