Cutaneous mastocytosis

Cutaneous mastocytosis is mastocytosis limited to the skin. CM accounts for about 90% of mastocytosis patients.  2/3 of CM cases are found in children and many will have resolution of skin lesions by puberty.  Adult onset CM tends to develop into systemic disease. 

There are several subtypes of CM.  All types are positive for Darier’s sign (redness and swelling due to local histamine release when touched.)  They are diagnosed by biopsy, which show an increased concentration of mast cells.  From this positive biopsy, they are differentiated based on the pattern of skin lesions.  The types of CM include:

Urticaria pigmentosa (UP)  is also called maculopapullar cutaneous mastocytosis (MPCM.)  This presentation is by far the most common.  UP is characterized by tan or red/brown lesions that usually start on the trunk and may eventually spread to other areas.  UP lesions are generally very itchy.  It is estimated that UP accounts for 65-90% of CM cases in children and 47-75% overall.  Systemic symptoms are sometimes seen in people with UP, and some patients develop SM.

Solitary mastocytomas comprise approximately 17-51% of CM cases and 10-35% of cases in children.  They are more common in children and are typically a single nodule on one of the limbs.  Multiple mastocytomas are unusual.  They often improve over time.

Diffuse cutaneous mastocytosis (DCM) is rare, accounting for 1-5% of CM in children.  DCM is the most severe presentation of CM.  It typically presents in early infancy and is almost always diagnosed before 3 years of age.  It involves lesions over a significant portion of the body, some of which may blister and bleed.  Thickening of the skin with age is common.  These patients often have systemic symptoms, including flushing, itching, low blood pressure, anaphylaxis, diarrhea and GI bleeding.

Telangiectasia macularis eruptive perstans is a rare form of CM found almost exclusively in adults.  Telangiectasia are small blood vessels near the surface of the skin or mucous membranes.  They are commonly called “spider veins.”  These lesions are smaller than UP lesions and generally don’t itch.  Some patients with TMEP develop SM.

Blistering can occur with any form of CM and is a function of mast cell burden in the skin.  Patients with prominent, frequent blistering are more likely to experience systemic symptoms and have a higher risk of anaphylaxis.