Mast Cell Activation Syndrome (MCAS) in Dogs & Cats
Mast cells are allergy cells responsible for immediate allergic reactions. They cause allergic symptoms by releasing products called “mediators” stored inside them or made by them. In allergic reactions, this release occurs when the allergy antibody IgE, which is present on the mast cell surfaces, binds to proteins that cause allergies, called allergens. This triggering is called activation, and the release of these mediators is called degranulation.
Some of these mediators are stored in granules in the mast cells and are released quickly and others are made slowly only after the cell has been triggered. Mast cells can also be activated by other substances, such as medications, infections, insect or reptile venoms. These responses, while not desirable, are made by “normal” mast cells. They are called “secondary activation” because they are due to (secondary to) external stimuli.
Sometimes mast cells become defective and release mediators because of abnormal internal signals. Certain mutations in mast cells can produce populations of identical mast cells – called clones – that overproduce and spontaneously release mediators. The spontaneous production of mediators in these clonal mast cell disorders is called “primary activation”. These abnormal cells can grow uncontrollably and are unusually sensitive to activation in a condition called mastocytosis.
Mast cells are a normal part of our immune system. They live in the bone marrow, flow through our blood stream and are located in every organ and connective tissue of the body. When mast cells detect stress, injury, toxins or infection, they release specific chemicals (mediators) which trigger an immune response. Think of them as sentries or guards.
When mast cells perform properly, they help us. When mast cells are agitated or over-reactive, the immune system goes haywire and starts to attack the body, triggering auto-inflammatory processes.
There are two major forms of mast cell activation diseases
- Mastocytosis— the abnormal accumulation of mast cells in one or more organ systems (cardiovascular, central nervous, digestive, endocrine, genitourinary, lymphatic, muscular, peripheral nervous, respiratory, dermatologic) which is diagnosed by a bone marrow biopsy or a genetic test.
- Mast cell activation syndromes (MCAS)— the inappropriate release of mast cell mediators including: histamine, interleukins, prostaglandins, cytokines, chemokines, and heparin (There are more than 200 chemical mediators associated with mast cells.)
Idiopathic Mast Cell Activation Syndrome
MCAS is a condition in which the patient experiences repeated episodes of the symptoms of anaphylaxis – allergic symptoms such as hives, swelling, low blood pressure, difficulty breathing and severe diarrhea. High levels of mast cell mediators are released during those episodes. The episodes respond to treatment with inhibitors or blockers of mast cell mediators. The episodes are called “idiopathic” which means that the mechanism is unknown – that is, not caused by allergic antibody or secondary to other known conditions that activate normal mast cells.
Evaluation for MCAS starts with determining whether the symptoms occur in separate attacks and are typical symptoms of an anaphylactic reaction without a clear cause. Mast cell mediators increase during the episode. Those mediators should be measured during acute episodes and at baseline looking for elevations during symptoms. Finally, the improvement with treatment using inhibitors of mast cell mediators completes the diagnosis.
Mast Cell Activation Syndrome (MCAS), which is an incurable disease, presented as repeated anaphylactic symptoms.
What are Mast Cells?
Found in the epithelial and mucosal tissues throughout the body, Mast Cells help regulate the formation of new blood cells, eliminate bacteria and parasites, and vasodilation as well as bone growth, and mineral homeostasis.
Mast Cells also regulate cell function in various cell types, including:
- Dendritic cells
- Macrophages
- T Cells
- B Cells
- Fibroblasts
- Eosinophils
- Endothelial Cells
- Epithelial Cells
While they’re very important parts of the body’s tissues, Mast Cells do produce and release substances which can be harmful in large quantities, including:
- Histamine
- Leukotrienes
- Heparin
- Proteases
- Prostanoids
- Cytokines
- Chemokines
- Growth factors
What Does Mast Cell Activation Syndrome look like?
There are a variety of symptoms associated with MCAS, including:
- Swelling of the body, either localised to one area, or general swelling.
- Nausea and vomiting
- Acute diarrhoea
- Hives
- Reduced/low blood pressure
- Difficulty breathing
- Difficulty swallowing
- Inability to stand or walk properly (may seem ‘drunk’)
If any of these symptoms shows, it is imperative to seek veterinary attention immediately. If these symptoms occur regularly, then your dog may need to undergo tests for Mast Cell Activation Syndrome.
What Causes Mast Cell Activation Syndrome?
It is unclear what causes MCAS to develop. It is often an idiopathic condition – meaning it happens without clinical reason.As it’s a condition related to allergies, it’s important to discover, and eliminate the allergens from the diet, to reduce the risk of triggers for the pet.One study suggests a possible link to the onset of MCAS, in patients with underlying immune disorders.
How Does the Vet Test for Mast Cell Activation Syndrome?
Blood tests will be carried out on your pet, to check for any elevated levels of histamines (which are released in the presence of a foreign body), tryptase (the markers of degeneration of mast cells, often produced during anaphylaxis), and prostaglandins (fatty compounds with a hormone-like effect in animals, which regulated inflammation).
If one, or all of these are present in abnormally elevated amounts, a diagnosis of MCAS may be given, particularly if these episodes are regular, and any prescribed antihistamines calm symptoms down.
The veterinarian may prescribe histamine 1 and 2 blockers, mast cell inhibitors, mast cell stabilisers, NSAIDs, immune suppressants, or other pharmaceuticals, which inhibit the production of histmaines and tyrosine.
One note to remember; some pharmaceuticals block DAO (Diamine Oxidase), which is the enzyme which breaks histamine down. We need histamine removed from the body as soon as possible so this is something to discuss with your veterinarian.
Compiled & Shared by- Team, LITD (Livestock Institute of Training & Development)
Image-Courtesy-Google
Reference-On Request.
