Proliferation of mast cells.  Can be restricted to skin or be systemic, with infiltration of bone marrow, spleen, liver and lymph nodes.  Systemic involvement not always obvious in the skin! Messy though, since mast cell mediators might act systemically even if mast cells themselves not widespread.

Systemic mastocytosis can present with episodic symptoms of dyspnoea, collapse (hypotension), reflux, diarrhoea.  Rather non-specific, so easily missed.  May also have hepatosplenomegaly, lymphadenopathy, osteoporosis, bone abnormalities.

Skin lesions may be present but not always dramatic (might just look like freckles).  May be history of dermatographism, recurrent itching, flushing and/or urticaria.  Different skin patterns seen, but overlapping:

• mastocytoma – slightly raised, can be slightly pigmented.  Physical irritation eg scratching causes flare and weal (Darier’s sign).  Can be present at birth, tend to be a good size eg 2-4cm nodule, may be blistering (in first 2 years of life only), else appear in first year of life.
• Urticaria Pigmentosa – usually presents in first 2 years of life, freckles or larger nodules/papules/plaques.  Can be blistering.  Resolves if not improves at puberty.
• Diffuse cutaneous mastocytosis (DCM) – no distinct lesions visible! Serious.
• Telangiectasia macularis eruptiva perstans (TMEP) –  brownish small macules with telangiectasia, generally in adults.  Can be systemic.

So look at skin, try Darier’s sign (not v sensitive).  Feel for liver and spleen.  Check Tryptase level (rarely normal even in systemic – compare baseline to peak, rather than just absolute level). Consider bone marrow biopsy to look for mast cells. Consider bone scan to look for abnormalities.  PCR for the D816V mutation in KIT gene?

Management

Control triggers (very individual):

• Stress (emotional/physical), sleep deprivation, pain
• Physical stimuation eg heat/cold, exercise/sex, sunlight, skin/scalp friction or trauma (tickling!)
• Bee/wasp stings
• Drugs esp aspirin/NSAIDs, opiates
• Alcohol

60% of kids resolve during puberty!

In later life there is a slightly higher risk of haematological disorders including cancer. There is also an increased risk of osteoporosis.

Stabilize mast cells:

• Anti-histamines, including H2 blockers.  Titrate dose to effect.
• Cromoglycate
• PUVA offers some temporary relief

Emergency treatment: Adrenaline auto-injectors for –

• systemic
• previous systemic reactions
• Extensive blistering lesions?

UK support group at www.ukmasto.org [Jess Hobart]

[Am Fam Physician. 1999 Jun 1;59(11):3047-3054.]