How do you diagnose Behçet syndrome in a young adult patient presenting with recurrent oral ulcers, genital ulcers, eye inflammation, skin lesions, and joint involvement?

Diagnosing Behçet Syndrome

Diagnose Behçet syndrome when this young adult has recurrent oral ulcers (mandatory) plus at least two of the following: recurrent genital ulcers, uveitis/retinal vasculitis, specific skin lesions (particularly erythema nodosum-like lesions), or positive pathergy test. 1

Essential Diagnostic Criteria

The diagnosis is primarily clinical and requires:

• Recurrent oral aphthous ulcers (mandatory criterion - must be present) 1
• Plus at least two of the following four criteria: 1
  • Recurrent genital ulceration (examine for active ulcers or scars from chronic ulceration) 1
  • Uveitis or retinal vasculitis (requires complete ophthalmologic examination) 1
  • Specific skin lesions (erythema nodosum-like lesions carry more diagnostic weight than papulopustular/acne-like lesions) 1
  • Positive pathergy test 1

Critical Clinical Evaluation Steps

Mucocutaneous Assessment

• Document frequency and pattern of oral ulcers (recurrent nature is essential) 1
• Perform thorough genital examination searching for active ulcers or scarring, as chronic genital ulceration can cause obliterative and deforming scarring 1
• Classify skin lesions: erythema nodosum-like lesions are more diagnostically significant than acneiform lesions 1

Mandatory Ophthalmologic Examination

• Complete ophthalmologic examination is mandatory to assess for uveitis or retinal vasculitis 1
• Ocular involvement is both a diagnostic criterion and a poor prognostic factor requiring urgent treatment 1
• Regular ophthalmologic follow-up is essential even after diagnosis 2

Organ-Specific Evaluations for Major Involvement

Eye inflammation (as in your patient):

• Formal ophthalmology consultation with slit-lamp examination 1

Joint involvement:

• Clinical examination for arthritis or arthralgia 2
• Joint involvement impairs quality of life but does not cause permanent damage 2

Vascular involvement (if suspected):

• Doppler ultrasound, CT angiography, or MR angiography 1
• Vascular involvement occurs in approximately one-third of patients 1

Neurological involvement (if suspected):

• MRI with contrast is the imaging modality of choice 1
• CSF analysis may show pleocytosis and elevated protein 1

Supportive Laboratory Tests

Inflammatory Markers

• ESR or CRP to monitor inflammatory activity (not specific but useful for monitoring) 1
• Complete blood count to check for anemia, leukocytosis, or thrombocytosis 1

HLA-B51 Testing

• HLA-B51 has moderate positive predictive value (~55%) and high negative predictive value (84-90%) 1
• Should not be used as standalone diagnostic test but rather as supportive evidence 1
• Useful when diagnosis is uncertain but clinical criteria are nearly met 1

Pathergy Test

• The only diagnostic test included in classification criteria 3
• Positive result supports diagnosis but negative result does not exclude it 1

Critical Differential Diagnoses to Exclude

Before confirming Behçet syndrome, rule out:

• Multiple sclerosis and neurosarcoidosis (if neurological involvement) 1
• Inflammatory bowel disease (Crohn's disease) 1, 4
• Sweet's disease 4
• Pemphigus 4
• Isolated erythema nodosum 4
• NSAID-induced ulcers 1
• Infections (tuberculosis, herpes simplex virus) 1, 4

Important Prognostic Considerations

Your patient has multiple poor prognostic features:

• Eye involvement (uveitis) indicates risk for serious damage and potential blindness if untreated 2
• Young adult presentation (disease typically appears in third-fourth decade) 5
• If male, particularly high risk for severe disease course requiring aggressive treatment 2

Immediate actions required:

• Rapidly suppress inflammation to prevent irreversible organ damage, especially vision loss 2
• Immunosuppressives are usually necessary for major organ involvement 2
• Multidisciplinary approach with ophthalmology is mandatory 2

Common Diagnostic Pitfalls

• Do not wait for all criteria to develop - early diagnosis and treatment prevent irreversible damage 2
• Do not dismiss acneiform lesions - while less diagnostically significant than erythema nodosum, they still count as skin involvement 1
• Do not rely solely on HLA-B51 - it is supportive evidence only, not diagnostic 1
• Do not overlook genital examination - patients may not volunteer this information; active searching for scars is essential 1
• Do not delay ophthalmology referral - ocular involvement requires urgent specialist evaluation to prevent blindness 2, 1