Pathergy test

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sahar Memar Montazerin, M.D.[2]
Synonyms and keywords: Pathergy

Overview

The pathergy test, is a non-specific skin or mucus membrane reaction to trauma that is observed in patients with Behçet disease. This reaction is classified as a hypersensitivity reaction. The positive pathergy test is one of the minor diagnostic criteria of Behçet’s disease.

Historical Perspective

Skin pathergy test was first reported by Blobner in 1937.

Procedure

Skin Pathergy test
There is no standardized method for performing the pathergy test. However, the method below is one of the suggested ways.
Procedure
The area of the skin should not be cleaned with disinfectant and the needle should be blunted against the inside surface of its sterile plastic sheath before using. The needle is inserted carefully at an angle of 30° to the skin into the dermis at a depth of 1.5–2 mm. The needle should not be observed beneath the epidermis and then it should be withdrawn with a twisting movement. The test is read between 24 to 48 hours after the procedure. One of the suggested scales for the degree of positivity is a three-point scale as follows:

• Negative Result: only needle mark (scored 0)
• Positive Result: the presence of papule or pustule
  • 1+ papule only
  • 2+ pustule

Another scale for the interpretation of the test, known as Dilsen pathergy test, is indicated in the table below:

Test result	Clinical characteristic of the needle mark at 48 h
Negative	Only erythema <2 mm
Undetermined	Only erythema >3 mm or papule 1-2 mm + erythema <2 mm
Positive	1+ Papule 2-3 mm + erythema >3 mm
	2+ Papule >3 mm + erythema >3 mm
	3+ Pustule 1-2 mm + erythema >3 mm
	4+ Pustule >2 mm + erythema >3 mm

To increase the sensitivity of the test:

• make at least two needle pricks on the glabrous skin of the forearm
• Use a large hypodermic needle (21 gauge or less)
• Use four needle pricks in total
• Use a blunt needle to prick

Oral pathergy test
To perform the test, a 20-gauge (0.9 mm) blunt disposable needle is used to prick the mucous membrane of the lower lip to the submucosa. The test is then read 48 hours later. The result is interpreted as below:

• Positive Result: Presence of pustule and/or ulcer
• Negative Result: Absence of aforementioned lesions

This method is more accessible than the traditional skin test, as there is no need to measure the size of the lesion and pustule or ulcer of any size turn the test positive. Additionally, it has similar sensitivity to Dilsen skin pathergy test.

Associated Conditions

The following disorders are associated with positive pathergy test:

• Behçet’s disease (the skin pathergy test is a specific diagnostic tool for this disorder)
• Pyoderma gangrenosum
• Sweet’s syndrome
• Atypical eosinophilic pustular folliculitis
• Neonates with Down syndrome
• Myeloproliferative disorders
• Non-Hodgkin’s lymphoma
• Chronic myeloid leukemia treated with interferon α
• Inflammatory bowel disease
• spondyloarthropathies (rarely)