Diffuse Cutaneous Mastocytosis

Diffuse cutaneous mastocytosis is a rare form of mastocytosis in infants, with widespread infiltration of the skin by mast cells. It carries a higher risk of blistering, severe symptoms and systemic reactions than other cutaneous forms.

Pathophysiology. Activating KIT variants cause mast cells to infiltrate the whole dermis, so the skin is thick, doughy and often red or yellow brown. Mediators released with friction, heat or infection cause itching, blistering and flushing, and can cause hypotension.

Onset is at birth or in the first months. Baseline tryptase is often raised, and systemic mastocytosis occurs in a minority.

Many infants improve with age, but severe early disease needs careful care.

• Diffuse erythema, thickened and doughy skin (pachydermic), peau d'orange appearance
• Bullae and blisters, often haemorrhagic, with minimal trauma
• Intense itching and irritability
• Flushing, diarrhoea and abdominal pain
• Hypotension and shock with severe episodes
• Failure to thrive in severe disease
• Dermographism and a generalised Darier sign

• Clinical examination: typical diffuse skin involvement in an infant, with a Darier sign.
• Skin biopsy: diffuse dermal mast cell infiltrate (toluidine blue, tryptase, CD117), which also excludes blistering diseases.
• Serum baseline tryptase: often raised. A level over 20 microgram/L needs systemic evaluation.
• KIT testing on skin or blood.
• Systemic assessment: full blood count, liver enzymes, abdominal ultrasound for organomegaly, and bone marrow biopsy if there are cytopenias, organomegaly or very high tryptase.
• Exclusion of infection and other blistering disease: skin swabs and, if needed, immunofluorescence biopsy.

Differential diagnosis.

• Staphylococcal scalded skin syndrome and bullous impetigo
• Epidermolysis bullosa and other congenital blistering disease
• Congenital erythroderma and ichthyosis
• Maculopapular cutaneous mastocytosis and systemic mastocytosis
• Langerhans cell histiocytosis
• Neonatal sepsis and Stevens-Johnson syndrome

• Admit infants with extensive blistering or any systemic symptoms for monitoring, since hypotension can occur quickly.
• Skin protection: non-adherent dressings, emollients, avoid friction and hot baths, and keep the infant cool.
• Trigger avoidance: avoid opioids, NSAIDs, aspirin and other mast cell triggering drugs unless needed. Plan vaccination with premedication and observation for 30 minutes.
• Antihistamine: cetirizine (children 1 to 5 years 2.5 mg twice daily; 6 to 11 years 5 mg twice daily), and a second agent or famotidine when needed.
• Topical corticosteroid: mometasone 0.1% cream once daily for 2 to 4 weeks on blistering areas, with wet wraps for severe disease.
• Sodium cromoglicate: 100 mg orally four times daily in children aged 2 to 12 years, for gastrointestinal symptoms.
• Severe blistering or shock: prednisolone 1 mg/kg orally or intravenously daily for 1 to 2 weeks and then tapered, and omalizumab in specialist care.
• Anaphylaxis or shock: adrenaline 0.01 mg/kg intramuscularly (maximum 0.5 mg) into the anterolateral thigh, repeated after 5 minutes if no improvement, with oxygen and fluids, and observation for at least 6 hours.
• Adrenaline auto injector and written plan for the family: 150 microgram for 7.5 to 25 kg, 300 microgram for 25 to 50 kg, 500 microgram for over 50 kg.
• Anaesthetic and procedural planning: premedication, avoid trigger agents, and monitor closely.
• Cytoreductive therapy (KIT inhibitor) is reserved for refractory life threatening disease in specialist centres.

Special groups.

• Newborns: avoid unnecessary adhesive dressings and sudden temperature changes.

Monitoring. Review every 1 to 3 months in infancy, with weight, skin and tryptase. Review every 6 months once stable, and during adolescence.

Referral and escalation. Refer to paediatric dermatology, allergy and haematology. Emergency for hypotension, collapse, or extensive blistering.