Mastocytosis

Mastocytosis is characterizedcharacterised by excessive accumulation of mast cells in one or more organs. According to the World Health Organizatiοn classification, three clinical entities fall under the mastocytosis umbrella: cutaneous mastocytosis, systemic mastocytosis (with or without cutaneous manifestations), and mast cell sarcoma. This article deals primarily with systemic mastocytosis.

Clinical presentation

There is considerable heterogeneity in the presentation of mastocytosis, and in the rate of disease progression. Clinical features include:

• cutaneous manifestations

• flushing

• hypotension and syncope

• urticaria pigmentosa

• abdominal pain

• nausea, vomiting and diarrhoea

• malabsorption

• bone pain and pathological fractures

• associated haematological disorders ⁷

Pathology

Mast cells are bone marrow-derived cells that are widely distributed in tissues. They store various biologically active mediators, such as heparin and histamine. Mediator release from mast cells has a central role in the development of type 1 hypersensitivity ¹. 

In systemic mastocytosis, abnormal proliferation and microscopic infiltration of mast cells involve the skin, bone marrow, gastrointestinal tract, liver and spleen. It is thought that the effects of mastocytosis relate at least in part to mediator release ⁷.

Classification

Under the 2016 revision of the WHO classification of tumours of haematopoietic and lymphoid tissues, mastocytosis is no longer considered a type of myeloproliferative neoplasm due to unique clinical and pathologic features.

There are multiple subtypes of systemic mastocytosis with varying clinical courses:

• indolent systemic mastocytosis (most common)

• smoldering

  smouldering systemic mastocytosis

• systemic mastocytosis with an associated hematologicalhaematological neoplasm

• aggressive systemic mastocytosis

• mast cell leukemialeukaemia

Radiographic features

Imaging findings are best categorised by the system rather than by modality. Most features are relatively non-specific but may suggest the diagnosis in the correct clinical setting.

Skeletal

Bone involvement in mastocytosis can be either lytic, sclerotic or mixed ^4,5. Diffuse involvement tends to be more common ¹¹. Usually, the radiographic appearance is that of sclerosis involving primarily the axial skeleton and the ends of the long bones. In some patients, there is generalised osteoporosis with the risk of pathological fractures.

Abdominal

• peptic ulcer disease

• diffuse small bowel thickening

• omental and mesenteric thickening ⁹

• hepatosplenomegaly

• ascites

• lymphadenopathy

Pulmonary

• pulmonary nodules (rare) ^2,8

See also

• differential diagnosis of diffuse bony sclerosis