Urticaria, commonly known as hives, is a skin reaction characterized by raised, intensely itchy welts. Pressure urticaria (PU) is a specific form of chronic inducible urticaria, meaning a physical stimulus consistently triggers it. This condition is defined by the development of painful, deep swelling in areas of the skin subjected to sustained pressure. Unlike typical hives, PU involves the deeper layers of the skin, resulting in a more profound and lasting reaction.
Identifying the Hives
The most distinguishing feature of pressure urticaria is its delayed onset. The reaction emerges hours after the pressure has been removed, typically beginning between 30 minutes and 12 hours after the stimulus, with four to six hours being common. The lesions differ significantly from ordinary hives, often resembling angioedema due to the involvement of deeper tissues. These swellings are reddened or discolored (erythematous) and are frequently described as painful or burning rather than itchy. Once they appear, these deep welts are persistent, often lasting for 8 to 72 hours before fading.
Common Causes and Triggers
The reaction is elicited by any prolonged or intense mechanical pressure exerted on the skin. This sustained force triggers the release of inflammatory mediators deep within the tissue, leading to delayed swelling. Affected areas are typically those parts of the body that bear weight or experience constant friction.
Common triggers include:
- Pressure from tight or restrictive clothing, such as a snug waistband or bra strap.
- Sitting on a hard surface for an extended period, affecting the buttocks and thighs.
- Prolonged standing or walking, causing swelling on the soles of the feet.
- Carrying heavy objects, such as a backpack or shopping bags, provoking swelling on the shoulders or hands.
Clinical Diagnosis
Diagnosis typically begins with a detailed patient history to establish a clear association between symptoms and a preceding pressure stimulus. Because symptoms are delayed and can resemble other conditions, the physician confirms the diagnosis using a controlled test.
This involves a diagnostic pressure challenge test, which applies a standardized weight to a specific area of the skin for a measured duration. The physician monitors the site, taking the definitive reading around six hours later to observe the delayed appearance of the characteristic swelling. Blood tests may also be ordered to rule out underlying systemic conditions, such as autoimmune disorders or urticarial vasculitis.
Treatment and Management Strategies
The primary medical approach involves using second-generation, non-sedating antihistamines, which are the recommended first-line pharmacological treatment. Because PU is often difficult to control, patients may require a dosage escalation, sometimes up to four times the standard licensed dose, for effective symptom suppression.
If symptoms remain poorly controlled despite high-dose antihistamine therapy, a specialist may introduce advanced treatments. The injectable biologic medication Omalizumab is an option for patients refractory to antihistamines. Other agents, such as Dapsone or a short course of systemic corticosteroids, may be considered for severe, persistent flares.
Management also requires meticulous avoidance of known mechanical triggers:
- Opt for loose-fitting clothing.
- Use supportive padding or cushioning when sitting or leaning.
- Change positions frequently and avoid prolonged standing.
- Modify activities or use ergonomic tools to reduce sustained pressure on the hands.