Did med cause skin condition?

Dear Dr. Gott: While in Vietnam, I was taking a dapsone pill daily, as the Army suggested. Unknown to me, I had an allergy to the pill and became methemoglobinemic. I stopped taking the pill, but still have lichen planus on my legs and buttocks that comes and goes. I can go weeks with no trouble, then I have a breakout that will last for up to a month before clearing. I read that the dapsone could be the cause of the onset of the lichen planus. Can you tell me if this is right or wrong? Where can I find more information?
Dear Reader: Dapsone is commonly prescribed to treat dermatitis, herpetiformis (a skin condition that commonly appears on the elbows and knees), acne, infection and more.
Lichen planus appears in the mouth or on the skin as an itchy, swollen rash. While its exact cause is unknown, it is thought to be related to an allergic or immune reaction, from exposure to specific medications, chemical substances that include gold rings or necklaces, hepatitis C and other causes.
Diagnosis is made through visual examination or skin-lesion biopsy. Once made, treatment might include antihistamines, lidocaine mouthwashes, topical corticosteroids, creams, ointments or ultraviolet-light therapy. The condition may last for an extended period, but is generally not harmful.
Methemoglobinemia is a blood disorder that occurs when an abnormal amount of a type of hemoglobin builds up in the blood. There are two inherited forms. The first is passed on by both parents, who don’t ordinarily have the condition themselves but carry a gene that causes it. The second form is known as hemoglobin M disease, caused by a defect in the hemoglobin molecule itself. In this case, only one parent passes on the abnormal gene.
The acquired type is more common than the inherited form and occurs following exposure to anesthetics, specific antibiotics and nitrates that are used as additives to prevent meat from spoiling.
Symptoms present with shortness of breath, headache, fatigue and a blue tint to the skin. The treatment of choice is methylene blue. Alternatives include exchange transfusions and hyperbaric-oxygen therapy.
From your brief explanation, my guess is that you were prescribed dapsone because of lichen planus. While you may have been allergic to the medication, I don’t believe it was the cause of your lichen planus but was the treatment of choice because of it. If I have misinterpreted your letter, we can take it up again at a later date.
To provide related information, I am sending you a copy of my Health Report “Blood — Donations and Disorders.” Other readers who would like a copy should send a self-addressed stamped No. 10 envelope and a $2 check or money order made payable to Newsletter and mailed to Newsletter, P.O. Box 167, Wickliffe, OH 44092-0167. Be sure to mention the title or print an order form off my website at