Physical urticarias, aquagenic pruritus, and cholinergic pruritus

Physical urticarias
About 25% of patients with chronic urticaria have a definable and reproducible physical trigger that distinguishes them from those with spontaneous urticaria and urticarial vasculitis. Physical urticarias are defined by the predominant stimulus that induces them (Table 181.1). More than one physical stimulus elicits urticaria in some patients, and physical urticarias can overlap with spontaneous urticaria. Physical urticarias are included under the term ‘inducible urticarias’ in the latest European classification.
Table 181.1
Classification of physical urticarias by the eliciting stimulus (in approximate reducing frequency of occurrence)
| Symptomatic dermographism | Stroking or rubbing the skin |
| Cholinergic urticaria (pale, papular wheals with red flares) | Rise in core temperature and other causes of sweating (exercise, hot baths, spicy food, and stress) |
| Cold urticaria | Rewarming of skin after cooling (localized or systemic) |
| Delayed pressure urticaria | Sustained perpendicular pressure |
| Solar urticaria | Ultraviolet or visible solar radiation |
| Localized heat urticaria | Local heat contact |
| Adrenergic urticaria (red papular wheals with surrounding pallor) | Emotional stress |
| Aquagenic urticaria | Local water contact at any temperature |
| Exercise-induced anaphylaxis | Exercise, but not hot baths |
| Food and exercise-induced anaphylaxis | Exercise following a heavy food load or eating specific foods |
| Vibratory angioedema | Vibration |
First-line therapies
Non-sedating antihistamines (Table 181.2) should be prescribed in preference to classical antihistamines, which are often sedating and can impair psychomotor performance. Up-dosing of second generation H1 antihistamines is often practiced.
Table 181.2
Examples of non- and mildly sedating antihistamines
| Acrivastine | Non-sedating, three-times-daily dosing |
| Cetirizine | Mildly sedating, once-daily dosing |
| Levocetirizine | The active enantiomer of cetirizine |
| Fexofenadine | Non-sedating, once-daily dosing |
| Loratadine | Non-sedating, once-daily dosing |
| Desloratadine | The active metabolite of loratadine |
| Mizolastine | Non-sedating, once-daily dosing |
| Rupatadine | Non-sedating, once-daily dosing |

Non-sedating (‘second generation’) antihistamines
H2 receptor antagonists
Narrowband UVB phototherapy
Photochemotherapy (PUVA)
Omalizumab
Danazol
Anticholinergics
Autologous sweat injection
Omalizumab
Cold tolerance (desensitization)
Leukotriene receptor antagonists
Antibiotics
Omalizumab
Omalizumab
Topical steroids
Leukotriene receptor antagonists
Sulfasalazine
Dapsone
Omalizumab
Induction of tolerance (phototherapy and photochemotherapy)
Omalizumab
β-Blockers
Epinephrine (adrenaline) cream
Intravenous immuneglobulins
Cyclosporine
Plasmapheresis
Etanercept
Explanation
Minimally sedating antihistamine
Sodium bicarbonate added to bath water
UVB
Narrowband UVB
Combined UVA/narrowband UVB therapy
Bath oil
Emulsifying ointment in the bath water
PUVA
Propranolol
Intramuscular triamcinolone
Transdermal nitroglycerin
Naltrexone 50 mg daily
Explanation
Second generation H1 antihistamines
Danazol