Reactive arthritis, formerly referred to as Reiter syndrome, is an idiopathic inflammatory process affecting the skin, joints, and mucous membranes. The classic triad of urethritis, conjunctivitis, and arthritis is found in only 40% of cases at the time of the initial clinical presentation.

Lesions and symptoms do not usually appear at the same time. Lesions may come on quickly and severely or more slowly, with sudden remissions or recurrences.

Reactive arthritis primarily affects sexually active males between the ages of 20 and 40. Those with human immunodeficiency virus (HIV) are at a particularly high risk (see Chapter 33: Cutaneous Manifestations of HIV Infection).

HLA-B27 is frequently positive in patients with reactive arthritis, which generally portends a poorer prognosis.

Skin lesions are often indistinguishable from psoriasis; however, reactive arthritis often manifests certain characteristic findings such as the following:

• Keratoderma blennorrhagicum (Fig. 34.42) consists of scaly, red, inflammatory, psoriasislike lesions on the palms and soles. The lesions may have a thick scale and may be pustular.

• Scaling red plaques or erosions may be found on the glans penis (circinate balanitis) (Fig. 34.43). Lesions may also be seen on the scalp, elbows, knees, and buttocks, shaft of the penis, and scrotum.

• Nail changes may include onycholysis and subungual hyperkeratosis (similar to psoriasis); furthermore, subungual pustules with resultant shedding of nails may occur.

• Oral lesions are usually painless, irregularly shaped, white plaques on the tongue that resemble geographic tongue.

Initial symptoms often occur after nongonococcal urethritis (e.g., chlamydial infection) or infection with an enteric pathogen (e.g., Shigella and Yersinia).

Reactive arthritis is a multisystemic disease that may present with fever, malaise, dysuria, arthralgias as well as red irritated eyes with accompanying cutaneous lesions.

Frequently, it has a self-limited course, but it may become a chronic, relapsing condition.

The arthritis of reactive arthritis is an asymmetric oligoarthritis that commonly involves large joints (elbows, knees); although it may also involve smaller joints. Sacroiliitis and ankylosing spondylitis may occur.

Ocular disease may include conjunctivitis with intense red conjunctival injection and, less commonly, iritis and keratitis.

Urethritis is a nonspecific urethral inflammation with a purulent exudate and dysuria.

The diagnosis is generally made on clinical grounds.

HLA-B27 is positive in 75% of patients.

ANA and rheumatoid factor are usually negative.

The histopathologic features of skin lesions are indistinguishable from those of psoriasis.

HIV testing should be performed.