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).
Histology:
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).
