Behcet Disease
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Direct answer
Recurrent oral ulceration occurring at least three times within twelve months plus any two of recurrent genital ulcers, eye lesions, skin lesions or a positive pathergy test defines Behcet disease by the International Study Group criteria. It is a vasculitis of both arteries and veins seen along the ancient Silk Road, including Turkey, the Middle East, Japan and parts of India, with a strong HLA-B51 association. The sight-threatening complications are posterior uveitis and retinal vasculitis, treated with azathioprine, cyclosporine or biologics, while colchicine handles mucocutaneous disease and glucocorticoids bridge flares.
What you must remember
- Oral aphthae are the universal opening symptom, histologically identical to simple aphthosis, so the diagnosis rests on what accompanies them.
- Genital ulcers are deeper, scar and are the most specific single supporting feature; skin lesions include erythema nodosum-like nodules, papulopustules and pseudofolliculitis.
- The pathergy test is a 20-gauge needle prick read at 24 to 48 hours; a sterile pustule is positive, reflecting skin hyperreactivity, and is most useful in Japanese and Turkish patients.
- Ocular disease is anterior or posterior uveitis with retinal vasculitis; hypopyon uveitis is the textbook image and untreated disease leads to blindness, often within five years.
- Neuro-Behcet is mostly a parenchymal brainstem or hemisphere lesion with headache and pyramidal signs; cerebral venous sinus thrombosis is the non-parenchymal form.
- Vascular Behcet uniquely causes both arterial aneurysms and venous thrombosis with normal clotting screens; superficial thrombophlebitis migrating up the leg is a recognised signal.
- HLA-B51 carries the strongest HLA association in rheumatology after HLA-B27 diseases; the male-to-female ratio and severity are higher along the Silk Road.
Approach to a young man with recurring mouth ulcers
A 27-year-old man from Kerala reports oral ulcers every two months for two years, a painful scrotal ulcer six months ago, and blurred vision in the right eye for a week. He has tender shin nodules and a history of a leg vein thrombosis.
Step one: map the criteria. Three-plus oral episodes within a year satisfy the obligatory criterion; genital ulceration with scarring, erythema nodosum-like lesions and uveitis provide three supporting items, so the International Study Group definition is met on history alone.
Step two: characterise the eye urgently. Slit-lamp examination defines anterior chamber inflammation and hypopyon; fundus fluorescein angiography assesses retinal vasculitis and macular involvement. Because retinal disease is the main cause of disability, any visual symptom warrants same-week ophthalmology.
Step three: complete the systemic survey. Skin pathergy testing where available, neurological examination, and imaging for venous sinus thrombosis if headache or papilloedema appear. Routine coagulation is normal, which is the point: thrombosis here is inflammatory, not thrombophilic.
Step four: treat by domain. Colchicine 0.5 to 1.5 mg daily for oral and genital ulcers and erythema nodosum; topical and intralesional steroids for oral ulcers; for eye disease, azathioprine plus steroids, cyclosporine or infliximab, since untreated posterior uveitis blinds; for neuro or vascular disease, high-dose steroids with cyclophosphamide or azathioprine. Anticoagulation decisions in venous thrombosis are individualised, with immunosuppression as the key intervention; immunosuppressed patients on anticoagulation need bleeding-risk assessment.
Step five: follow for the known relapsing course, tapering nothing abruptly. Male sex, young age at onset and frequent flares predict severity; the mortality drivers are neurologic and large-vessel disease and bowel perforation.
Where the exam tries to catch you
The standard confusion is with simplex aphthosis and Behcet mimics: coeliac disease, inflammatory bowel disease, cyclic neutropenia, HIV and lupus all ulcerate mouths, so the exam answer hinges on the company the ulcers keep. Genital scarring, pathergy, hypopyon uveitis or a normal coagulation screen with thrombosis push you towards Behcet. The second trap is in ophthalmology stems: unilateral alternating recurrent uveitis in a young Asian man with mouth ulcers is Behcet until excluded, while the HLA-B27 group shows an acute alternating anterior uveitis with spondyloarthritis. Note also that steroids alone are insufficient for ocular and neurological disease and may even increase flares when used long term without a steroid-sparing agent.
Frequently asked questions
How many oral ulcers episodes per year are required by the ISG criteria?
Three or more recurrences within twelve months, which is the mandatory entry criterion.
What is a positive pathergy test?
A sterile pustule or papule appearing 24 to 48 hours after a standard needle prick, reflecting cutaneous hyperreactivity.
Which HLA allele associates with Behcet disease?
HLA-B51, the classic Silk Road haplotype association.
Which drug is first-line for mucocutaneous ulcers?
Colchicine, with topical steroids for acute oral ulcers and apremilast as an emerging option.
Why can Behcet cause thrombosis with a normal coagulation profile?
Because the thrombosis is vasculitic and inflammatory rather than a clotting factor abnormality, so immunosuppression, not just anticoagulation, drives treatment.
What distinguishes neuro-Behcet thrombosis from multiple sclerosis?
Brainstem-plus parenchymal involvement, headache, meningeal enhancement and the mucocutaneous background, against dissemination in time and space with oligoclonal bands.