DermatologyTier 2Disease (DEADMAN)

Cutaneous manifestations of systemic disease - Behçet disease

Description

Variable-vessel vasculitis - arteries AND veins, any size
- The only vasculitis with no size restriction - Chapel Hill puts it in its own category
Relapsing-remitting, multisystem; no diagnostic test - clinical diagnosis

Domains

Mucocutaneous - oral + genital ulcers, papulopustular lesions, erythema nodosum-like
Ocular - uveitis (sight-threatening)
Vascular - thrombosis (venous) and pseudoaneurysm (arterial)
Neuro - parenchymal brainstem disease, cerebral venous sinus thrombosis
GI - ileocaecal ulceration, mimics Crohn's
Joints - non-erosive mono/oligoarthritis

Silk Road distribution - Turkey (highest prevalence worldwide), Middle East, Iran, Japan, Korea, China
- Rare in Northern Europe and Australia (mostly migrant populations)
Onset 20-40 yrs
M=F overall, but males and younger onset = more severe disease
- Male sex predicts ocular, vascular and neuro involvement
Severity declines with age and disease duration

*HLA-B51** - strongest genetic association, tracks the Silk Road distribution
- Present in many healthy people in endemic regions - not a diagnostic test
Environmental trigger (Streptococcus sanguinis, oral microbiome) in a genetically primed host
Th1/Th17 skew -> inc IL-17, IL-1beta, TNF-alpha
Neutrophil hyperfunction -> pathergy, sterile pustules
Endothelial activation + neutrophilic infiltration of vessel wall
- Venous -> thrombosis (inflammatory thrombus, adherent to wall, rarely embolises)
- Arterial -> aneurysm/pseudoaneurysm (pulmonary artery aneurysm = most lethal lesion)

International Study Group criteria

Recurrent oral ulceration (>=3x/yr) - mandatory, PLUS >=2 of:
- Recurrent genital ulceration
- Eye lesions (uveitis, retinal vasculitis)
- Skin lesions (erythema nodosum, pseudofolliculitis, papulopustular, acneiform in a post-adolescent not on steroids)
- Positive pathergy test
ICBD (2014) point-based criteria are more sensitive - oral 2, genital 2, ocular 2, skin 1, neuro 1, vascular 1, pathergy 1; score >=4 = Behçet

Pathergy test

Sterile 20G needle prick to forearm -> papule/pustule at 24-48 h
Highly specific; sensitivity is population-dependent (high Turkey/Japan, low in Northern Europeans)

Discriminators

Feature	Behçet
Oral ulcers	First and most frequent feature; painful, recurrent
Genital ulcers	Scrotum/labia, scar - aphthae elsewhere usually do not
Uveitis	Panuveitis, hypopyon, retinal vasculitis, bilateral
Vascular	Lower-limb DVT commonest; also Budd-Chiari, CVST, pulmonary artery aneurysm
Neuro (5-10%)	Parenchymal brainstem lesion; CSF pleocytosis
GI	Deep ileocaecal ulcers; mainly Asian populations; faecal calprotectin tracks activity

Tests

Inflammatory markers often only mildly raised - do not track disease well
ANA/ANCA/RF negative; serology is for excluding mimics
CTPA if haemoptysis - pulmonary artery aneurysm, not PE (anticoagulating it is fatal)
MRI brain + MRV for neuro-Behçet

Treat by organ involved and prognostic risk, not by a single ladder.

A. Mucocutaneous + joint

Colchicine first-line (erythema nodosum, genital ulcers, arthritis)
Topical steroid / sucralfate for oral ulcers
Refractory: apremilast (specific evidence for oral ulcers), azathioprine, TNF-alpha inhibitor
Short steroid bursts for flares - not maintenance

B. Ocular

Sight-threatening posterior uveitis/retinal vasculitis -> systemic steroid + azathioprine, and early infliximab or adalimumab
- Alternative: interferon-alpha
Topical steroid alone is inadequate for posterior segment disease

C. Vascular

Immunosuppression, not anticoagulation, is the primary treatment of Behçet thrombosis
- Steroid + azathioprine/CYC; TNF inhibitor if refractory
- Thrombus is inflammatory and adherent -> embolisation and recanalisation are both uncommon
Exclude pulmonary artery aneurysm before anticoagulating - anticoagulation there causes fatal haemoptysis
Arterial aneurysm: immunosuppression + surgical/endovascular repair

D. Neuro-Behçet

Parenchymal: high-dose steroid -> azathioprine/MMF; TNF inhibitor for severe or refractory
CVST: steroid; anticoagulation only after aneurysm excluded
Avoid ciclosporin in neuro-Behçet - neurotoxic and associated with CNS involvement

E. GI

Steroid + azathioprine/5-ASA; TNF inhibitor or thalidomide if refractory
Surgery only for perforation/obstruction/uncontrolled bleeding (high anastomotic recurrence)

HLA-B*51
Other HLA-B27-negative "MHC-I-opathies" - psoriasis, AS (shared IL-17/IL-23 biology)
Pregnancy - disease often quiescent; thrombotic risk persists
MDS with trisomy 8 - associated with intestinal Behçet-like disease
Amyloid A (AA) amyloidosis - rare, late

Relapsing-remitting; activity tends to burn out over years
Prognosis driven by male sex + young age at onset and by organ involvement
Mortality mainly from:
- Pulmonary artery aneurysm rupture (highest mortality single lesion)
- Major vessel arterial disease, Budd-Chiari
- Neuro-Behçet (parenchymal, progressive form)
Ocular: blindness in untreated posterior uveitis; modern biologic therapy has markedly reduced this
Monitor: eyes (regular ophthalmology), vascular symptoms, neurological change

6 more sections, plus exam facts

Premium unlocks every note across every specialty, and the full exam fact library behind it.