Dermographism

Symptomatic dermographism (dermographic urticaria, factitious urticaria) is the commonest form of chronic inducible urticaria. Light stroking, scratching, rubbing or pressure on the skin triggers a linear itchy weal and flare within minutes, because of local mast cell degranulation.

• It affects 2 to 5% of the population, mostly young adults (peak 20 to 40 years). The condition lasts for several years (average 2 to 5 years) and often resolves spontaneously, though some patients have it for much longer.
• Mechanism: mast cell release of histamine in response to mechanical stress. IgE autoantibodies against unidentified antigens and a passive transfer reaction by serum have been shown.
• Associations and triggers: infections, drugs (penicillin, other antibiotics, NSAIDs), thyroid disease, scabies, emotional stress, hormonal change, and mastocytosis. Sometimes it follows an acute urticaria.
• Simple (physiological) dermographism, with a weal but no itch, occurs in up to 5% and needs no treatment.

• Linear red raised weals, with surrounding flare, in the shape of the stimulus (including writing on the skin), appearing within 1 to 5 minutes of friction, peaking at 5 to 10 minutes, and fading within 15 to 60 minutes.
• Itch is intense and worse in the evening, with night time itching related to friction from clothing and bedding. Sites under tight clothes, belts, straps and waistbands, as well as the back and arms, are commonly affected.
• Delayed dermographism: a deep, tender swelling appearing 3 to 8 hours after pressure and lasting up to 48 hours (pressure urticaria).
• Differential diagnosis: chronic spontaneous urticaria (weals appear without trigger, last up to 24 hours), cholinergic urticaria (small weals with sweating), cold and pressure urticaria, urticarial vasculitis (weals last more than 24 hours, leave bruising), mastocytosis (urticaria pigmentosa with positive Darier sign), scabies, atopic dermatitis and contact urticaria.
• Complications: sleep loss, reduced quality of life, anxiety, and rare angioedema. It does not cause anaphylaxis.

• Provocation test: stroke the skin of the forearm or upper back firmly with a tongue depressor, a blunt pen, or a dermographometer. A weal with flare within 10 minutes confirms the diagnosis. A dermographometer defines the threshold (for example a spring loaded pin at 36 g/mm2 or lower).
• Baseline tests are limited: full blood count with differential, CRP or ESR, and thyroid function with thyroid antibodies.
• Look for triggers: stool for parasites when relevant, hepatitis B and C, and scabies examination.
• Serum tryptase if mastocytosis is suspected (urticaria pigmentosa, flushing, gastrointestinal or bone symptoms), with skin biopsy when needed.
• Skin biopsy and tests for vasculitis (ANA, complement C3 and C4) if weals persist beyond 24 hours or leave bruising.

• Avoid triggers, wear loose soft clothes, avoid tight straps and rough fabrics, use cool showers, keep nails short, and avoid vigorous towelling. Stop suspect drugs (NSAIDs, opioids, aspirin) where possible. Treat scabies and thyroid disease if present.
• First line therapy: a non-sedating H1 antihistamine, taken daily and not only when symptomatic. Licensed doses are used first, and then increased up to 4 times the licensed dose if symptoms persist after 2 to 4 weeks (specialist guided, off label):
  • Cetirizine 10 mg orally once daily, up to 40 mg daily (child 6 to 11 years 5 to 10 mg daily, 2 to 5 years 2.5 mg 12 hourly).
  • Levocetirizine 5 mg daily, up to 20 mg daily.
  • Fexofenadine 180 mg daily, up to 720 mg daily.
  • Bilastine 20 mg daily, up to 80 mg daily.
  • Desloratadine 5 mg daily, up to 20 mg daily.
  • Rupatadine 10 mg daily, up to 40 mg daily.
  • Loratadine 10 mg daily, up to 40 mg daily.
  • Take the higher dose at night if drowsiness occurs. Reduce the dose in renal impairment (for example cetirizine 5 mg daily when creatinine clearance is below 30 mL/min).
• Second line therapy:
  • Add a sedating antihistamine at night: hydroxyzine 10 to 25 mg, or doxepin 10 to 25 mg (limited evidence and anticholinergic effects).
  • Ketotifen 1 mg orally 12 hourly, or montelukast 10 mg orally at night (evidence limited).
  • Narrowband UVB phototherapy 3 times weekly for 4 to 8 weeks, which may reduce mast cell reactivity.
  • Omalizumab 150 to 300 mg subcutaneously every 4 weeks, for patients who do not respond to high dose antihistamines (evidence for inducible urticaria is moderate, and use is often off label in some regions).
  • Short courses of oral prednisolone are not recommended for long term treatment.
• Cool compresses, calamine and menthol lotions reduce the itch. Avoid topical steroids, which do not help.
• Special groups:
  • Pregnancy: cetirizine and loratadine have the most safety data. Avoid doxepin, ketotifen and high doses of antihistamines unless advised, and avoid omalizumab unless the benefit outweighs the risk.
  • Children: weight based non-sedating antihistamines, and avoid sedatives.
  • Elderly: avoid sedating antihistamines (confusion, falls, urinary retention).
  • Renal and hepatic impairment: reduce antihistamine doses.
• Follow up: review at 2 to 4 weeks and step up treatment. Once controlled for 3 to 6 months, reduce the dose gradually. Refer to dermatology or allergy if there is no response to 4 times the licensed dose of antihistamine, systemic features, or suspected mastocytosis.