The most likely diagnosis is Behçet syndrome, a form of vasculitis that can affect small to large arterial vessels and is one of the few forms of vasculitis that also can affect veins. Behçet syndrome has an increased prevalence in a belt from East Asia to Turkey and therefore conveys an ethnic/genetic risk in those with a Mediterranean/Asian background. Behçet syndrome is characterized by recurrent painful oral ulcers plus at least two of the following: recurrent painful genital ulcers, eye involvement, skin involvement (typically acneiform lesions), and pathergy (development of a pustule following a needle stick). Oral ulcers typically resolve spontaneously after 1 to 3 weeks. Eye involvement can be severe, especially when there is a posterior uveitis/retinal vasculitis, and can lead to blindness. Hypopyon (suppurative fluid seen in the anterior chamber) is also a distinctive feature. The combination of recurrent painful oral ulcerations, genital ulcerations, and uveitis make Behçet syndrome the most likely diagnosis in this patient. Other clinical findings include gastrointestinal ulceration that may make it challenging to differentiate Behçet syndrome from Crohn disease with extraintestinal manifestations. Arthritis affecting medium and large joints is common, and the vasculitic process may cause neurologic, cardiopulmonary, kidney, and vascular complications.

Clinical manifestations of cytomegalovirus infection (CMV) include a mononucleosis-like illness with findings ranging from fever and lymphadenopathy to colitis, hepatitis, and even retinitis. Oral ulcers, genital ulcers, and hypopyon are not features of acute CMV infection.

Herpes simplex virus type 1 (HSV-1) infection has been classically associated with causing recurrent painful oral ulcerations. Although HSV-1 is being increasingly recognized as a cause of genital ulceration, it is much less common than with HSV type 2 infection. Systemic symptoms, such as fever, may be associated with primary herpes virus infection but are less common with recurrent episodes of viral activation. Additionally, HSV-1 may also be associated with ocular disease, although keratitis is the most common manifestation seen with HSV-1 infection and not hypopyon, as seen in this patient.

Reactive arthritis (formerly known as Reiter syndrome) is a postinfectious, noninfectious arthritis that occurs in both men and women. Arthritis, usually oligoarticular, develops several days to weeks after a genitourinary or gastrointestinal infection and can be associated with oral and genital lesions as well as uveitis. Unlike Behçet, the oral ulcers are painless, the genital lesions are hyperkeratotic rather than ulcerative, and hypopyon is not typical.