Differential Diagnosis for Drug-Induced Rash
Single Most Likely Diagnosis
- Morbilliform Drug Rash: This is the most common type of drug-induced rash, accounting for approximately 90% of cases. It is characterized by a maculopapular rash that typically appears 7-14 days after starting a new medication. The rash is often symmetric, starting on the trunk and spreading to the extremities.
Other Likely Diagnoses
- Urticarial Drug Rash: This type of rash is characterized by itchy, raised wheals that can appear anywhere on the body. It is often associated with allergic reactions to medications such as penicillin or NSAIDs.
- Fixed Drug Eruption: This is a type of rash that occurs at the same site every time the offending medication is taken. It is often characterized by a well-demarcated, circular patch of skin that is red, blistered, or crusted.
- Photosensitive Drug Rash: This type of rash occurs when a medication reacts with sunlight to cause a skin reaction. It is often characterized by a rash that appears on sun-exposed areas of the body.
Do Not Miss Diagnoses
- Stevens-Johnson Syndrome (SJS): This is a life-threatening condition that is characterized by a severe skin and mucous membrane reaction. It is often associated with medications such as sulfa antibiotics, anticonvulsants, and NSAIDs. SJS can progress to toxic epidermal necrolysis (TEN) if not recognized and treated promptly.
- Drug Rash with Eosinophilia and Systemic Symptoms (DRESS): This is a rare but potentially life-threatening condition that is characterized by a skin rash, fever, lymphadenopathy, and internal organ involvement. It is often associated with medications such as anticonvulsants, sulfa antibiotics, and NSAIDs.
- Toxic Epidermal Necrolysis (TEN): This is a severe skin condition that is characterized by widespread skin necrosis and detachment. It is often associated with medications such as sulfa antibiotics, anticonvulsants, and NSAIDs.
Rare Diagnoses
- Acute Generalized Exanthematous Pustulosis (AGEP): This is a rare condition that is characterized by a sudden onset of pustules on the skin. It is often associated with medications such as beta-lactam antibiotics and macrolides.
- Erythema Multiforme: This is a rare condition that is characterized by a skin rash with target lesions. It is often associated with medications such as sulfa antibiotics, anticonvulsants, and NSAIDs.
- Serum Sickness-Like Reaction: This is a rare condition that is characterized by a skin rash, fever, and lymphadenopathy. It is often associated with medications such as cefaclor and penicillin.