Mast cells are a type of white blood cell that play a role in the body’s immune system, particularly in allergic responses and inflammation. These cells are found throughout the body, acting as a kind of alarm system against foreign invaders. A mast cell tumor develops when these cells grow abnormally and become cancerous, forming masses that can appear in various locations. Degranulation refers to the process where mast cells, whether normal or cancerous, release their stored chemical substances.
Understanding Mast Cells and Tumors
Mast cells originate in the bone marrow and then travel through the bloodstream to mature in various tissues. They are particularly abundant in areas exposed to the external world, such as the skin, respiratory tract, and gastrointestinal tract. In their normal function, mast cells contain granules, which hold chemical mediators. When activated, typically by allergens or pathogens, these cells release their contents to help defend the body. This process contributes to immune responses, such as wound healing and defense against parasites.
When mast cells become cancerous, they form tumors that can appear as lumps or bumps on or under the skin. These tumors can also develop internally, affecting organs like the spleen, liver, intestines, and bone marrow. Mast cell tumors are recognized by their tendency to often fluctuate in size. This fluctuation is often linked to the release of their contents.
The Process of Degranulation
Degranulation is the process where mast cells release chemical mediators stored in their granules into the surrounding tissue. These mediators include substances like histamine, heparin, proteases, and cytokines. Histamine, for example, causes symptoms like itchiness, redness, and swelling in allergic reactions. The rapid release of these compounds can happen within seconds of stimulation.
Degranulation in mast cell tumors can be triggered by several factors. Physical manipulation of the tumor, such as bumping it or even during a veterinary examination like a fine-needle aspiration, can trigger degranulation. Stress, pain, or sudden temperature changes can also trigger degranulation. Sometimes, degranulation may occur spontaneously without any obvious external stimulus. This excessive release of mediators by cancerous mast cells leads to various clinical signs.
The Impact of Degranulation
When mast cell tumors degranulate, the released chemical mediators cause a range of effects, both localized around the tumor and systemically throughout the body. Locally, the area around the tumor can experience swelling, redness, and itching due to histamine. Bruising can also occur, sometimes referred to as Darier’s sign, indicating degranulation. The tumor itself might appear to swell and become more prominent, then shrink again, a characteristic fluctuating appearance.
Beyond local reactions, the mediators can enter the bloodstream and cause systemic issues. Gastrointestinal upset is a common systemic effect, including vomiting, diarrhea, loss of appetite, and sometimes melena (dark, tarry stools from internal bleeding) due to stomach or intestinal ulcers. In severe cases, widespread mediator release can lead to low blood pressure (hypotension) and, rarely, life-threatening anaphylactic shock. Other effects include delayed wound healing, bleeding disorders, and, in advanced stages, tumor spread to internal organs like lymph nodes, spleen, and liver, causing enlargement.
Managing Degranulation Episodes
Managing degranulation episodes focuses on alleviating symptoms caused by released mediators. Avoiding physical manipulation of the tumor, and preventing licking, chewing, or scratching the tumor, can help reduce the frequency of degranulation. An Elizabethan collar might be recommended to prevent self-trauma.
Medications often counteract degranulation effects. Antihistamines, like diphenhydramine (an H1 blocker), block histamine effects, reducing itching, swelling, and other allergic symptoms. H2 receptor blockers, like famotidine, reduce stomach acid and address gastrointestinal issues such as nausea and abdominal pain. Corticosteroids may also be used to reduce inflammation. These supportive treatments improve comfort and manage degranulation’s immediate effects, rather than directly treating the tumor.