From the Guidelines

Delayed pressure urticaria is the diagnosis for pressure urticaria.

The weals of physical urticaria, including delayed pressure urticaria, usually last less than 1 h, except for delayed pressure urticaria which takes 2-6 h to develop and up to 48 h to fade 1
Delayed pressure urticaria is a type of physical urticaria that is triggered by mechanical stimuli, specifically pressure 1
It is characterized by swellings that are induced rather than spontaneous and can be distinguished from other types of urticaria by its unique duration and triggers 1
The diagnosis of delayed pressure urticaria can be made based on the clinical presentation and duration of individual weals, without extensive investigation 1
It is essential to distinguish delayed pressure urticaria from other types of urticaria, such as urticarial vasculitis, which presents with small vessel vasculitis histologically and may have joint and renal involvement 1

From the Research

The diagnosis of pressure urticaria can be made through a combination of clinical evaluation and diagnostic tests.

A thorough history taking is essential to identify the association between pressure-related symptoms and the preceding physical stimulus 2.
Pressure challenge tests, such as the dermographometer test or the weighted rod test, can be used to diagnose delayed pressure urticaria (DPU) 2, 3.
Skin biopsy may also be performed to confirm the diagnosis, with characteristic findings including deep dermal inflammatory infiltrate of neutrophils and eosinophils 4, 3.
The autologous serum skin test may also be positive in some cases of DPU 3.

The diagnostic criteria for pressure urticaria include:

The development of deep swellings at sites of pressure application on the skin 5.
A delay of several hours between the application of pressure and the appearance of symptoms 4.
The presence of erythematous, often painful swellings at sites of sustained pressure on the skin 4.
Resistance to antihistamines and other non-steroidal medications 3.

Pressure urticaria is a relatively rare condition, with an estimated incidence of 22% in patients with chronic urticaria 2.

It is more common in patients with chronic idiopathic urticaria, with up to 40% of patients affected 4.
The condition may be underdiagnosed due to the difficulty in recognizing the association between pressure-related symptoms and the preceding physical stimulus 2.