Urinary tract infection as a cause of lichen planus: metronidazole therapy.

A 51-year-old woman with generalized lichen planus for 23 years experienced total involution of her lesions during metronidazole therapy. Discontinuance of the treatment on two occasions led to partial recurrence of the skin lesions, which again promptly cleared on reinstitution of metronidazole. It is believed that this patient's lichen planus was an immune reaction to circulating bacterial antigen. The presumed source was a chronic urinary bladder infection. Continued remission of the lichen planus and the cystitis was subsequently achieved for over a year by daily prophylactic nitrofurantoin therapy. Identification and eradication of chronic foci of infection are suggested for the management of generalized chronic lichen planus.