Patients experience a mild, brief illness; complaints include fever, malaise, headache, and pruritus. The characteristic erythema appears about 10 days later. Facial redness is similar to that which occurs when a child is slapped; however, circumoral redness is absent. Several days following initial erythema, a less distinct rash may appear on the extremities and trunk. The rash usually resolves within 1 week but may occur for several weeks when the patient is exposed to heat, cold, exercise, or stress. Adults may also experience arthralgia and arthritis although these symptoms are less common in children. In addition, mild transient anemia, thrombocytopenia, and leukopenia may develop.
The central nervous system (CNS) is the most common site of extracutaneous involvement in children. Cerebellar ataxia is the most frequently encountered syndrome. Other possible CNS complications include encephalitis, meningitis, transverse myelitis and, rarely, Reye's syndrome (especially subsequent to aspirin use). Varicella pneumonia and encephalitis can be serious complications in adults. Additional rare complications in children and adults include myocarditis, corneal lesions, nephritis, arthritis, bleeding diatheses, acute glomerulonephritis and hepatitis. 1 , 2 , 7 , 21
Recurrent erythema multiforme is usually treated initially with continuous oral aciclovir for 6 months at a dose of 10 mg/kg/d in divided doses (eg, 400 mg twice daily), even if HSV has not been an obvious trigger for the patient's erythema multiforme. This has been shown to be effective in placebo-controlled double blind studies. However, erythema multiforme may recur when the aciclovir is ceased. Other antiviral drugs such as valciclovir (500–1000 mg/d) and famciclovir (250 mg twice daily) should be tried if aciclovir has not helped; these drugs are not readily available in New Zealand.