How  is Behcet's Disease Diagnosed? 

There is no specific “Behcet’s test”.  Consequently, the diagnosis is based on the occurrence of symptoms and signs that are compatible with the disease, the presence of certain features that are particularly characteristic (e.g., oral or genital ulcerations), elimination of other possible causes of the patient’s presentation, and — whenever possible — proof of vasculitis by biopsy of an involved organ.

An international group of physicians has established a set of guidelines to aid in the classification of Behcet’s patients for  the purpose of conducting research in the disease. The criteria put forth by the group include  recurrent oral ulceration (at  least three occasions in a year).  In addition, a patient must also meet two of the following four criteria for Behcet’s disease:  recurrent genital ulcerations,  eye lesions (uveitis or retinal vasculitis),  skin lesions (erythema nodosum, lesions, acne), and or  positive "pathergy test". 

The  pathergy test is a simple test in which the forearm is pricked with a small, sterile needle. Occurrence of a small red bump or pustule at the site of needle insertion  constitutes a positive test. Although a positive pathergy test is helpful in the diagnosis of Behcet’s,  only a minority of Behcet’s patients demonstrate the pathergy phenomenon (i.e., have positive tests). Patients from the Mediterranean region are more likely to demonstrate pathergy.  In addition, other conditions can occasionally result in positive pathergy tests, so the test is not 100% specific.