This patient should discontinue the trimethoprim-sulfamethoxazole, and a complete blood count and liver chemistry tests should be ordered. She has a widespread morbilliform eruption with fever, facial edema, and lymphadenopathy that started 6 days after taking trimethoprim-sulfamethoxazole. This is typical of a systemic drug hypersensitivity syndrome, otherwise known as drug reaction with eosinophilia and systemic symptoms (DRESS) syndrome. It is a rare, potentially life-threatening drug-induced hypersensitivity reaction. The presentation of DRESS typically includes a skin eruption, hematologic abnormalities, lymphadenopathy, and internal organ involvement (including the liver, kidneys, and lungs). The presence of DRESS should be suspected in patients with a morbilliform rash, fever, facial swelling, and lymphadenopathy that occur 5 to 10 days after starting a potentially offending medication. The initial diagnostic approach in suspected DRESS is to assess for evidence of systemic organ involvement, and this is accomplished by obtaining a complete blood count, which may show atypical lymphocytosis and eosinophilia, and liver chemistry studies, which may show aminotransferase elevations. Patients with extensive cutaneous reactions or evidence of organ involvement may require hospitalization and possibly treatment with systemic glucocorticoids. Even if the rash fades, the patient can still progress to liver failure.
Lymph node biopsy may show a range of findings that may be suspicious for lymphoma. Lymph node biopsy is rarely required for the diagnosis or management of DRESS.
Skin biopsy may show lymphocytic infiltration and edema in DRESS and may confirm the diagnosis, although it is not helpful in assessing the severity of systemic organ involvement.
No further testing following discontinuation of the likely causative medication is appropriate in patients without evidence of significant organ involvement. However, exclusion of significant systemic involvement is necessary before a supportive approach is taken.
