Pressure Urticaria Workup

Updated: Jan 25, 2019
  • Author: Sarah Beggs, MD; Chief Editor: Dirk M Elston, MD  more...
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Workup

Laboratory Studies

An elevated white blood cell (WBC) count or neutrophilia may be present. [25, 26] Complement levels are normal.

Some patients with delayed pressure urticaria (DPU) also have concomitant chronic idiopathic urticaria (CIU). Basic testing for CIU includes CBC count with differential, erythrocyte sedimentation rate, and/or C-reactive protein. Extended diagnostic testing includes the following [20, 27] :

  • Thyroid function tests and antibody testing for autoimmune thyroid disease

  • Antibody testing for Helicobacter pylori 

  • Autoantibody to IgE 

  • Allergy testing (skin tests and/or allergen avoidance tests)

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Pressure Challenge Testing

Pressure challenge testing (with the dermographometer or the suspended-weight method) may be performed for delayed pressure urticaria (DPU). Because therapy may influence test results, it is recommended that testing be performed at a time when therapy has been interrupted or stopped for at least 3 days; however, some patients may have more severe disease that does not allow this. Repetitive testing can be used to assess response to therapy.

Multiple methods of applying measured amounts of pressure can be used to test for the development of DPU. A consensus conference review suggests using the following approaches [20] :

  • A shoulder strap 3 cm wide with a 7-kg weight for 15 minutes

  • A rod 1.5 cm in diameter with a 2.5-kg weight for 15 minutes

  • A rod 6.5 cm in diameter with a 5-kg weight for 15 minutes

  • A dermographometer to a pressure of 100 g/mm2 for 70 seconds

The tests are most often applied to the shoulders, upper back, posterior thighs, or volar forearm. Pressure provocation tests should be read at 6 hours. Both the weight and the application time should be recorded. The duration of application is inversely related to the pressure applied; for example, wheals take longer to develop with a lower pressure than with a higher pressure.

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Histologic Findings

The histologic features of delayed pressure urticaria (DPU) lesions are variable, often depending on the age of the lesion. Biopsy within hours demonstrates moderate-to-heavy infiltration of eosinophils with neutrophils and lymphocytes in a perivascular and interstitial pattern in the dermis and subcutaneous fat. Degranulated mast cells may be noted. Biopsy of an older DPU lesion (>24 h) demonstrates eosinophils and lymphocytes.

No vessel-related changes (eg, leukocytoclasia or fibrinoid necrosis), such as those noted in urticarial vasculitis, are seen. Direct immunofluorescence test results are negative.

Several reports of bullous pressure urticaria have been reported, and histologic findings show spongiosis and intraepidermal bullae associated with an eosinophil-rich inflammatory infiltrate in the superficial and deep dermis. [10]

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