Mastocytosis, a type of mast cell disease, is a rare disorder affecting both children and adults caused by the accumulation of functionally defective mast cells (also called mastocytes) and CD34+ mast cell precursors. People affected by mastocytosis are susceptible to a variety of symptoms, including itching, hives, and anaphylactic shock, caused by the release of histamine and other pro-inflammatory substances from mast cells.
Signs and symptoms
When mast cells undergo degranulation, the substances that are released can cause a number of symptoms that can vary over time and can range in intensity from mild to severe. Because mast cells play a role in allergic reactions, the symptoms of mastocytosis often are similar to the symptoms of an allergic reaction. They may include, but are not limited to
Fatigue Skin lesions (urticaria pigmentosa), itching, and dermatographic urticaria (skin writing) "Darier's Sign", a reaction to stroking or scratching of urticaria lesions. Abdominal discomfort Nausea and vomiting Diarrhea Olfactive intolerance Ear/nose/throat inflammation Anaphylaxis (shock from allergic or immune causes) Episodes of very low blood pressure (including shock) and faintness Bone or muscle pain Decreased bone density or increased bone density (osteoporosis or osteosclerosis) Headache Depression Ocular discomfort Increased stomach acid production causing peptic ulcers (increased stimulation of enterochromaffin cell and direct histamine stimulation on parietal cell) Malabsorption (due to inactivation of pancreatic enzymes by increased acid) Hepatosplenomegaly There are few qualitative studies about the effects of mastocytosis on daily life. However, a Danish study from 2018 describes the multidimensional impact of the disease on everyday life.
Pathophysiology Mast cells are located in connective tissue, including the skin, the linings of the stomach and intestine, and other sites. They play an important role in the immune defence against bacteria and parasites. By releasing chemical "alarms" such as histamine, mast cells attract other key players of the immune defense system to areas of the body where they are needed. Mast cells seem to have other roles as well. Because they gather together around wounds, mast cells may play a part in wound healing. For example, the typical itching felt around a healing scab may be caused by histamine released by mast cells. Researchers also think mast cells may have a role in the growth of blood vessels (angiogenesis). No one with too few or no mast cells has been found, which indicates to some scientists we may not be able to survive with too few mast cells. Mast cells express a cell surface receptor, c-kit (CD117), which is the receptor for stem cell factor (scf). In laboratory studies, scf appears to be important for the proliferation of mast cells. Mutations of the gene coding for the c-kit receptor (mutation KIT(D816V)), leading to constitutive signalling through the receptor is found in >90% of patients with systemic mastocytosis.
Diagnosis Diagnosis of urticaria pigmentosa (cutaneous mastocytosis, see above) can often be done by seeing the characteristic lesions that are dark brown and fixed. A small skin sample (biopsy) may help confirm the diagnosis. In case of suspicion of systemic disease the level of serum tryptase in the blood can be of help. If the base level of s-tryptase is elevated, this implies that the mastocytosis can be systemic. In cases of suspicion of SM help can also be drawn from analysis of mutation in KIT(D816V) in peripheral blood using sensitive PCR-technology To set the diagnosis of systemic mastocytosis, certain criteria must be met. Either one major + one minor criterion or three minor criteria has to be fulfilled:
Major criterion Dense infiltrates of >15 mast cells in the bone marrow or an extracutaneous organ
Minor criteria Aberrant phenotype on the mast cells (pos. for CD2 and/or CD25) Aberrant mast cell morphology (spindle-shaped) Finding of mutation in KIT(D816V) S-tryptase >20 ng/ml
Other mast cell diseases Other types of mast cell disease include:
Monoclonal mast cell activation, defined by the World Health Organization definitions 2010, also has increased mast cells but insufficient to be systemic mastocytosis (in World Health Organization Definitions) Mast cell activation syndrome – has normal number of mast cells, but all the symptoms and in some cases the genetic markers of systemic mastocytosis Mast cell sarcoma
Classification Mastocytosis can occur in a variety of forms:
Cutaneous mastocytosis (CM) The most common cutaneous mastocytosis is maculopapular cutaneous mastocytosis, previously named papular urticaria pigmentosa (UP), more common in children, although also seen in adults. Telangiectasia macularis eruptiva perstans (TMEP) is a much rarer form of cutaneous mastocytosis that affects adults.[2] MPCM and TMEP can be a part of indolent systemic mastocytosis. This should be considered if patients develop any systemic symptoms Generalized eruption of cutaneous mastocytosis (adult type) is the most common pattern of mastocytosis presenting to the dermatologist, with the most common lesions being macules, papules, or nodules that are disseminated over most of the body but especially on the upper arms, legs, and trunk Diffuse cutaneous mastocytosis has diffuse involvement in which the entire integument may be thickened and infiltrated with mast cells to produce a peculiar orange color, giving rise to the term homme orange. Cutaneous mastocytosis in children usually presents in the first year after birth and in most cases vanishes during adolescence.
Systemic mastocytosis (SM)
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