Characterized by the triad of urethritis, uveitis, and arthritis +/- mucocutaneous lesions.
Clinical: males in 3rd - 4th decades; endemic form is often associated with new sexual partner followed by urethritis; epidemic form may be secondary to enteric infections (90% of patients with epidemic form also have urethritis, so don't use this as a means of distinguishing between endemic and epidemic types).
Causative agents: chlamydia trachomatis is most common agent; also: gonorrhea, ureaplasma urealyticum, shigella flexneri, salmonella species, campylobacter species, yersinia enterocolitica.
Genetics: 60-80% are HLA-B27 positive.
Genital involvement: balanitis circinata (painless lesion that begins as a red papule but enlarges to form a ring-like lesion, image A & image B) and keratoderma blennorrhagica (erythematous macules on the palms and soles).
Psoriasiform hyperplasia (epidermis becomes thickened with broad rete pegs) and pustule formation.
Hyperkeratosis, parakeratosis (pink keratin debris on top of the skin contains pyknotic nuclei).