BD disease, formally known as Behçet’s disease (also spelled Behçet syndrome), is a chronic inflammatory condition that causes blood vessel inflammation throughout the body. It affects arteries and veins of all sizes, which is why its symptoms can show up in so many different places, from painful mouth sores to serious complications in the eyes, brain, and cardiovascular system. The hallmark symptoms are recurrent oral ulcers and genital ulcers, but the disease can be far more wide-ranging than those surface-level signs suggest.
What Causes Behçet’s Disease
The exact cause remains unknown, but Behçet’s is classified as an auto-inflammatory disease, meaning the immune system attacks the body’s own blood vessels without a clear trigger. The process is driven by overactive immune cells. Specific white blood cells ramp up and release a flood of inflammatory signals that damage blood vessel walls and surrounding tissue. This leads to the ulcers, skin lesions, and organ damage that define the disease.
Genetics play a measurable role. Carrying a specific immune system gene called HLA-B51 increases the risk of developing Behçet’s by nearly sixfold, according to a large meta-analysis of over 4,800 cases. That association holds across ethnic groups worldwide, making it one of the strongest known genetic links to the disease. Still, most people who carry the gene never develop Behçet’s, so other environmental or immune factors are clearly involved.
Who Gets It
Behçet’s disease follows a striking geographic pattern. It is most common along the ancient Silk Road trade routes, stretching from East Asia through the Middle East and into the Mediterranean. Turkey has by far the highest prevalence at roughly 421 cases per 100,000 people. Iran follows at about 80 per 100,000, then Saudi Arabia (20), Iraq (17), Israel (15), and Japan (14). In Western Europe and North America, the disease is comparatively rare.
Both men and women develop Behçet’s, typically between the ages of 20 and 40. Men tend to have more severe vascular and eye complications, while women are somewhat more likely to develop genital ulcers and certain skin lesions.
The Main Symptoms
Oral ulcers are nearly universal, occurring in about 97% of patients regardless of sex. These aren’t ordinary canker sores. They tend to be larger, more painful, and recur frequently, sometimes appearing in clusters inside the cheeks, on the gums, or on the tongue. For many people, mouth sores are the first symptom and may precede other signs by years.
Genital ulcers are the second most common feature, affecting roughly 65 to 71% of patients. In women, they typically appear on the vulva; in men, on the scrotum. These ulcers can be deep and painful, and they often leave scars.
Skin problems show up in several forms. Acne-like eruptions (papulopustular lesions) are especially common in men, appearing in about 53% of male patients compared to 22% of women. Tender, red nodules on the shins, called erythema nodosum, affect about 25 to 37% of patients.
Eye inflammation is one of the more serious features. Chronic, relapsing inflammation inside the eye can lead to vision loss if untreated. This typically affects both eyes over time and is a major driver of long-term disability in Behçet’s patients.
Vascular Complications
Because Behçet’s targets blood vessels directly, vascular problems are common and potentially dangerous. About 40% of patients develop vascular involvement at some point, and it tends to be more frequent and severe in men.
Venous blood clots are the most typical vascular complication. Deep vein thrombosis in the legs accounts for 60 to 80% of all vascular events in Behçet’s patients. Unlike ordinary blood clots, these are driven by vessel wall inflammation rather than sluggish blood flow, which changes how they’re managed.
Arterial complications are less common but more dangerous. Aneurysms, where a weakened artery wall balloons outward, can form in the aorta, pulmonary arteries, or leg arteries. Arterial blockages and narrowing also occur. These vascular events are one of the leading causes of death in Behçet’s patients.
When the Brain Is Involved
Neurological involvement, sometimes called neuro-Behçet’s, occurs in roughly 5 to 20% of patients and usually develops one to ten years after the first symptoms appear. It is one of the most serious complications of the disease.
The inflammation tends to target the brain’s white matter and brainstem. This can cause severe headaches, confusion, personality changes, difficulty with coordination, weakness on one side of the body, and seizures. Some patients develop blood clots in the veins that drain the brain, leading to dangerous increases in pressure inside the skull. In rare cases, the disease causes cognitive decline over time. Neurological involvement, alongside major vascular disease, is the primary driver of mortality in Behçet’s.
How It’s Diagnosed
There is no single blood test or imaging study that confirms Behçet’s disease. Diagnosis relies on a point-based scoring system called the International Criteria for Behçet’s Disease (ICBD). Six clinical features are evaluated, each assigned a point value:
- Genital ulcers: 2 points
- Eye inflammation: 2 points
- Oral ulcers: 1 point
- Skin lesions: 1 point
- Vascular involvement: 1 point
- Positive pathergy test: 1 point
A score of 3 or more points leads to a diagnosis. Notably, oral ulcers are not required. A patient with genital ulcers and eye inflammation alone would meet the threshold.
The pathergy test is a simple skin-prick procedure where a needle is inserted into the forearm. In people with Behçet’s, the skin overreacts, forming a red bump or pustule at the puncture site within 24 to 48 hours. The test is most useful in countries along the Silk Road, where positivity rates range from 50 to 88%. In the U.S. and U.K., fewer than 20% of confirmed Behçet’s patients test positive, which limits its diagnostic value in those populations.
Treatment and Long-Term Outlook
Treatment is tailored to which organs are affected. Mild disease involving mainly mouth and genital ulcers is typically managed with medications that calm the immune response and reduce inflammation. When the eyes, brain, or blood vessels are involved, more aggressive immune-suppressing therapy is needed to prevent permanent damage.
The disease follows a relapsing-remitting pattern for most people: symptoms flare, improve, and flare again over months or years. The severity of flares often decreases with age, and many patients find the disease becomes more manageable over time.
For the majority of patients, Behçet’s does not shorten life. In one long-term study of over 400 patients, the overall mortality rate was about 10%, with deaths concentrated among men who had developed major vascular disease or neurological complications. The 10-year mortality in milder cases was closer to 4%. Early, consistent treatment of eye and vascular disease has significantly improved outcomes compared to previous decades.