What conditions enter the differential diagnosis of an “Lichen planus-like” eruption?

Lichenoid drug eruptions may be indistinguishable from idiopathic LP. Any exogenous ingestant, or rarely a topical chemical, may be causative. Common etiologic agents are listed in Table 12-1. Other potables, such as alcoholic liqueurs containing gold particles, have been implicated in lichenoid eruptions. Contact with certain chemicals, particularly those involved with photodeveloping, may result in a lichenoid contact dermatitis. Clues suggesting a lichenoid drug eruption include an atypical distribution or lack of mucosal involvement. Histopathologic clues to a drug-induced eruption include significant parakeratosis and eosinophils within the inflammatory infiltrate.

Ellgehausen P, Elsner P, Burg G: Drug-induced lichen planus, Clin Dermatol 16:325–332, 1998.

Table 12-1. Common Etiologic Drug Classes in LP-like Drug Eruptions
	Antihypertensives Beta-blockers ACE inhibitors Thiazides Furosemide Methyldopa Antimicrobials Acyclovir Isoniazid Tetracyclines Antiinflammatory agents Nonsteroidal anti-inflammatory drugs Gold salts Sulfones		Antimalarials Chloroquine Quinacrine Anticonvulsants Carbamazepine Phenytoin Neurologic agents Benzodiazepines Phenothiazines Lipid-lowering agents Lovastatin Fluvastatin Biologic response modifiers Tumor necrosis factor α antagonists (infliximab, etanercept, adalimumab) Imatinib mesylate		Miscellaneous Sulfonylureas Chlorpropamide Allopurinol Penicillamine Sildenafil Misoprostol