Behcet Disease
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Direct answer
Behcet disease is a variable vasculitis of unknown cause that presents with recurrent oral ulcers plus at least two further features: genital ulcers, eye involvement, skin lesions or a positive pathergy test. Oral aphthous ulcers at least three times in 12 months are the mandatory entry point in International Study Group criteria. Eye disease, especially posterior uveitis, carries the greatest risk of permanent vision loss and needs early immunosuppression.
What you must remember
- Oral ulcers: recurrent painful aphthous ulcers, at least three times a year, form the mandatory criterion and are the commonest presenting feature.
- Genital ulcers: deep, painful ulcers on the scrotum or labia that heal with scarring, unlike simple aphthae.
- Eye involvement: anterior and posterior uveitis, hypopyon and retinal vasculitis, with posterior disease carrying the worst visual prognosis.
- Skin lesions: erythema nodosum-like nodules, papulopustular and acneiform lesions, which support the diagnosis but are not diagnostic alone.
- Pathergy test: a sterile needle prick produces a papule or pustule when read at 24 to 48 hours, and it is more often positive in Middle Eastern and Mediterranean populations.
- HLA-B51: an association that supports the diagnosis but is neither required nor specific.
- Management: colchicine and topical steroids for mucocutaneous disease, with azathioprine, ciclosporin or anti-TNF agents for eye and vascular disease.
- Serious complications: deep vein thrombosis in young men, intracardiac disease and neurological involvement need prompt specialist review.
Where the exam tries to catch you
Three traps recur, and each one treats a systemic disease as a trivial one.
- Trap: labelling recurrent oral ulcers as simple aphthosis when genital ulcers are present. Correct: painful genital ulcers with recurrent oral ulcers form the Behcet pattern and warrant a full criteria check.
- Trap: treating a red eye with steroid drops alone without specialist review. Correct: posterior uveitis in Behcet disease needs systemic immunosuppression, because topical drops do not control posterior disease.
- Trap: reading a negative pathergy test as proof of absence. Correct: pathergy is supportive only, and its positivity varies by population, so the clinical criteria still decide the diagnosis.
Frequently asked questions
What are the mandatory criteria for diagnosing Behcet disease?
Recurrent oral aphthous ulceration at least three times in 12 months is the mandatory criterion in the International Study Group criteria. A diagnosis then requires two of the following: recurrent genital ulcers, eye lesions, skin lesions or a positive pathergy test.
Why is uveitis in Behcet disease treated more aggressively than ordinary uveitis?
Posterior uveitis and retinal vasculitis in Behcet disease cause recurrent attacks that can lead to irreversible vision loss. Such eye disease usually needs systemic immunosuppression, such as azathioprine, ciclosporin or anti-TNF agents, rather than topical drops alone.
What does a positive pathergy test show in Behcet disease?
A positive pathergy test shows an exaggerated skin reaction, a papule or pustule, at a sterile needle-prick site after 24 to 48 hours. It supports the diagnosis of Behcet disease but is not required for it, and its frequency varies across populations.
Which conditions mimic Behcet disease in a patient with oral ulcers?
Herpes simplex infection, inflammatory bowel disease such as Crohn disease, coeliac disease and drug-induced ulcers can all mimic Behcet disease. A careful history, examination and targeted tests are needed before the diagnosis of Behcet disease is accepted.