Introduction

• Cause: pressure applied to the skin. In some cases, certain foods may sensitize the skin’s reaction to pressure.
• Signs: wheals or edema in areas of skin where an external source produced pressure, eg tack.
• Diagnosis: history, typical clinical presentation, exclusion of differentials, confirmation “drawing” in the patient with a blunt object.
• Treatment: avoidance of etiologic factors when possible. Standard treatment for urticaria, eg antihistamines, corticosteroids, fatty acids. Allergen specific immunotherapy.
• Prognosis: favorable as general health is not usually compromised.

Pathogenesis

Etiology

• The etiology is unknown, it can be associated with atopy Skin: atopy.
• Pressure applied on skin evokes the reaction.
• In some cases, some foods may trigger the reaction if administered before the pressure.
• In humans, respiratory tract infections, hepatitis, diabetes mellitus, stress and drug reactions are associated with dermatographism.

Predisposing factors

General

• Food reactions, drug reactions and environmental factors are thought to predispose the skin to this response.

Specific

• Specific underlying factors can often be difficult to identify.

Pathophysiology

• Cutaneous reaction following a suspected mechano-immunologic trigger.
• Regardless of the cause, mast cell degranulation occurs. Sensitization by IgE is suspected in humans.
• Basophils, macrophages and other cells release bioactive molecules, eg histamine, platelet-activating factor and prostaglandins.
• Their effects include vascular smooth muscle relaxation and retraction of endothelial cells that result in plasma extravasation → edema (wheal).

Timecourse

• Lesions appear within minutes following the exposure to pressure.
• Delayed dermatographism reported in humans (not horses) when urticaria takes hours to develop.

Epidemiology

• Urticarial reactions are usually specific to the individual.

Diagnosis

Treatment

Prevention

Outcomes