What is cutaneous mastocytosis?

Cutaneous Mastocytosis

Cutaneous mastocytosis is a rare disorder characterized by abnormal accumulation of mast cells limited to the skin, typically presenting in early childhood with various skin lesions and mediator-related symptoms that can significantly impact quality of life and, in severe cases, pose life-threatening risks. 1, 2

Types of Cutaneous Mastocytosis

1. Urticaria Pigmentosa (UP) / Maculopapular Cutaneous Mastocytosis

• Most common form (70-90% of cases)
• Presents as multiple red-brown to yellow macules, plaques, or nodules
• Typically appears within first year of life (80% by 6 months)
• Primarily affects trunk and extremities, sparing palms, soles, scalp, and face
• Positive Darier's sign (urtication and flare upon rubbing lesions)
• Tends to resolve spontaneously by age 10 1

2. Mastocytomas

• Accounts for 10-35% of cases
• Single or several nodular lesions, larger than UP (up to several cm)
• Often present at birth or within first week of life
• Can vesiculate and blister
• Positive Darier's sign
• Most resolve by puberty 1

3. Diffuse Cutaneous Mastocytosis (DCM)

• Rare (1-3% of cases) but most severe form
• Involves entire skin with central region and scalp most affected
• Can appear at birth or early infancy
• Presents with blistering, bullae (often hemorrhagic), leathery/thickened skin
• Associated with higher risk of systemic symptoms and complications
• Can lead to life-threatening hypotensive episodes 1, 3

4. Telangiectasia Macularis Eruptiva Persistans (TMEP)

• Least common form, rarely presents in childhood
• Red telangiectatic macules in tan/brown background
• Can coexist with UP 1

Pathophysiology

• Characterized by increased numbers of mast cells in the papillary dermis
• In UP, mast cells aggregate around blood vessels, sometimes with eosinophils
• In nodular forms, mast cells may infiltrate entire dermis and subcutaneous tissues
• Mast cell numbers can be 10 times higher than normal skin
• Many children do not present with c-kit mutations found in adult mastocytosis
• When present, mutations may include Asp816Val, Asp816Phe, and others 1, 2

Clinical Manifestations

Skin Symptoms

• Positive Darier's sign (urtication and flare upon rubbing)
• Flushing (20-65% of patients)
• Pruritus
• Dermatographism
• Swelling, redness
• Blistering/bullae (especially in DCM) 1, 2

Systemic Symptoms (Due to Mast Cell Mediator Release)

• Gastrointestinal: abdominal pain, diarrhea (up to 40% of children)
• Cardiovascular: hypotension, tachycardia (rare in UP, more common in DCM)
• Respiratory: wheezing, shortness of breath
• Anaphylaxis (rare but possible in all forms)
• Whole body flushing
• In severe DCM: intestinal bleeding, anemia, hypovolemic shock 1, 2

Diagnosis

Clinical Evaluation

• Physical examination with assessment of Darier's sign
• Evaluation of skin lesion characteristics and distribution
• Assessment of associated symptoms 1, 2

Laboratory Tests

• Serum tryptase (may be elevated, especially in extensive disease)
• Complete blood count with differential
• Histamine metabolites in urine 1, 2

Skin Biopsy

• Essential for definitive diagnosis
• Staining with hematoxylin & eosin and giemsa
• Immunostaining for tryptase and KIT
• Analysis of c-kit mutations when possible 1

Bone Marrow Studies

• Recommended if:
  • Significantly elevated tryptase
  • Severe systemic symptoms
  • Associated organomegaly
  • Poor response to initial therapy 1, 2

Natural History

• Most cases present in first year of life (41.8% before 6 months)
• Strong tendency for spontaneous resolution before puberty
• 75% of mastocytomas and 56% of UP cases show complete resolution
• Lesions appearing after age 10 tend to persist and remain symptomatic
• DCM may have more prolonged course with higher risk of complications 1

Management Approach

General Measures

• Identify and avoid triggers:
  • Temperature changes
  • Physical exertion
  • Emotional stress
  • Alcohol
  • Certain foods
  • Medications
  • Insect stings 1, 2

Pharmacological Treatment

• First-line: Antimediator therapy

  • H1 antihistamines (for pruritus, flushing)
  • H2 antihistamines (for gastrointestinal symptoms)
  • Mast cell stabilizers 1, 4

• For localized lesions:

  • Short-term topical corticosteroids
  • Topical calcineurin inhibitors (e.g., pimecrolimus) 5, 4

• For severe cases (particularly DCM):

  • Systemic corticosteroids
  • Phototherapy (PUVA) - may provide temporary relief in DCM
  • Omalizumab
  • Tyrosine kinase inhibitors (in extremely severe cases) 3, 4

Emergency Preparedness

• Epinephrine autoinjector for patients with:
  • History of anaphylaxis
  • DCM
  • Persistently elevated serum tryptase 4

Prognosis

• Generally favorable in pediatric cutaneous mastocytosis
• Most cases resolve spontaneously by puberty
• DCM has higher risk of complications and may require more aggressive management
• Symptoms typically more severe in first 6-18 months after onset 1, 3

Important Considerations

• Multidisciplinary approach involving dermatologists, allergists, and hematologists is beneficial
• Regular follow-up every 6-12 months is recommended
• Parents should be informed about the possibility of evolution to systemic form in a minority of cases
• Diagnosis may be challenging due to rarity and overlap with other skin conditions 1, 6