Cutaneous Drug Reactions
Cutaneous reactions are among the most frequent medication toxicities. These can have a wide range of severity and manifestations including urticaria, photosensitivity, erythema multiforme, fixed drug reactions, erythema nodosum, vasculitis, lichenoid reactions, bullous drug reactions, Stevens-Johnson syndrome, and toxic epidermal necrolysis (TEN). Diagnosis is usually made by appearance and careful medication history.
Erythema Multiforme is a reaction pattern of skin consisting of a variety of lesions but most commonly erythematous papules and bullae. “Target” or “iris” lesion is characteristic and consists of concentric circles of erythema and normal flesh-colored skin, often with a central vesicle or bulla. Distribution of lesions is classically acral, especially. palms and soles. The most common causes are drug reaction (particularly penicillins and sulfonamides) or concurrent herpetic or Mycoplasma infection. It can rarely affect mucosal surfaces and internal organs (erythema multiforme major or Stevens-Johnson syndrome).
Erythema nodosum is septal panniculitis characterized by erythematous, warm, tender subcutaneous nodular lesions typically over anterior tibia. Lesions are usually flush with skin surface but are indurated and have appearance of an erythematous/ violaceous bruise. Lesions usually resolve spontaneously in 3–6 weeks without scarring. Commonly seen in sarcoidosis, administration of certain drugs (esp. sulfonamides, oral contraceptives, and estrogens), and a wide range of infections including streptococcal and tubercular; may be idiopathic.
Lichen planus is a disorder of unknown cause. It can follow administration of certain drugs and in chronic graft-versus-host disease. The lesions are pruritic, polygonal, flat-topped, and violaceous. Its course is variable, but most patients have spontaneous remissions 6–24 months after onset of disease.
Pityriasis rosea is a self-limited condition lasting 3–8 weeks. Initially, there is a single 2- to 6-cm annular salmon-colored patch (herald patch) with a peripheral rim of scale, followed in days to weeks by a generalized eruption involving the trunk and proximal extremities. Individual lesions are similar to but smaller than the herald patch and are arranged in symmetric fashion with long axis of each individual lesion along skin lines of cleavage.
Disorder is self-limited, so treatment is directed at symptoms.
Urticaria is a common disorder, either acute or chronic, characterized by evanescent (individual lesions lasting <24 h), pruritic, edematous, pink to erythematous plaques with a whitish halo around margin of individual lesions. Lesions range in size from papules to giant coalescent lesions (10–20 cm in diameter). It is often due to drugs, systemic infection, or foods (esp. shellfish). Food additives such as tartrazine dye, benzoate, or salicylates have also been implicated.
Palpable purpura (nonblanching, elevated lesions) is the cutaneous hallmark of vasculitis. Other lesions include petechiae (esp. early lesions), necrosis with ulceration, bullae, and urticarial lesions (urticarial vasculitis). Lesions are usually most prominent on lower extremities. Vasculitis may be associated with infections, collagen-vascular disease, primary systemic vasculitides, malignancy, hepatitis B and C, drugs (especially thiazides), and inflammatory bowel disease. It may occur as an idiopathic, predominantly cutaneous vasculitis.