Pathergy test

**Pathergy phenomenon is defined as a state of altered tissue reactivity that occurs in response to minor trauma like a needle prick (with a blunt needle)

**Pathogenesis of pathergy phenomenon
Although the exact mechanisms underlying pathergy phenomenon are unknown, skin injury caused by needle prick apparently triggers a cutaneous inflammatory response and creates a papule/pustule. This suggests an increased or aberrant release of cytokines from keratinocytes or other cells in the epidermis or dermis. The specificity of skin pathergy reaction is very high especially in Behcets disease (about 99%), especially when it is positive at 48 h

**Types of pathergy tests

1) Oral Pathergy test: Pricking the oral mucosa with a needle and looking at ulcer creation

Oral Pathergy test- Pricking with a 20- gauze needle.

Positive test: Ulcer formation at 48 hrs

2) Skin Pathergy test:  2 needle pricks with 20 gauge needle are given on the flexor aspect of the forearms at an angle of 30 degree till 1.5 mm depth. Readings are taken after 48 hrs of the needle prick. A 1-2mm papule that is usually felt by palpation and which is surrounded by an erythematous halo is formed on the skin. The papule may remain as a papule or transform into a pustule. The pustule becomes prominent in 24 h, becomes maximum in size in 48 h, and disappears in 45 days. Erythema without induration is interpreted as a negative result. Histopathology of the new lesion demonstrates inflammation with mononuclear cells.

**Seen in
1) Behcet's disease- Positive pathergy reaction is very important for the diagnosis of Behcet's disease in patients with only recurrent oral ulceration plus one of the other criteria (recurrent genital ulceration, eye lesions, skin lesions). The test has also been used as an indicator of disease activity in patients with Behcet's disease. It is one of the 4 minor criteria in its diagnosis
2) Pyoderma gangrenosum
3) Rheumatoid arthritis
4) Inflammatory bowel disease
5) Eosinophilic pustular folliculitis
6) Healthy individuals
7) Sweets syndrome- rare but described

Ref: Sequeira FF, Daryani D. The oral and skin pathergy test. Indian J Dermatol Venereol Leprol 2011;77:526-30

MCQs

1) Pathergy test is most characteristic of
a. Behcets disease
b. Dermatitis herpetiformis
c. Sweet syndrome
d. Pyoderma gangrenosum
Answer: a

2) A patient presents with recurrent painful oro-genital ulcers. The test which will help in leading to a diagnosis is
a. Oral biopsy
b. Genital biopsy
c. Pathergy test
d. Eye examination

Answer: c
Expl: Positive pathergy reaction is very important for the diagnosis of Behcet's disease in patients with only recurrent oral ulceration plus one of the other criteria (recurrent genital ulceration, eye lesions, skin lesions)

3) What is false about pathergy test (PGI type)

a. Screening test for Behcets disease
b. Indicator of disease activity in Behcet's disease
c. Double prick is better than a single prick
d. Independent risk factor for occurrence of postoperative complications in Behcet's disease.
e. Sharp needle increases the positivity rate

Answer: a. e

Expl: The low sensitivity of pathergy test prevents it from being used as a screening test. Use of a blunt (reusable, sterilized) needle increases the frequency and intensity of a positive skin pathergy test as it is more traumatic.