Differential Diagnosis for Drug Rash

• Single most likely diagnosis:
  • Morbilliform drug eruption: This is the most common type of drug rash, accounting for approximately 90% of cases. It is characterized by a maculopapular rash that resembles measles, often appearing within a week of starting a new medication. The rash typically starts on the trunk and spreads to the limbs, and it can be accompanied by systemic symptoms such as fever and malaise.
• Other Likely diagnoses:
  • Urticarial drug eruption: 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 type of rash is characterized by well-defined, circular patches that recur at the same site each time the offending medication is taken. Common culprits include sulfonamides, tetracyclines, and NSAIDs.
  • Photosensitive drug eruption: This type of rash occurs when certain medications react with sunlight to cause a skin reaction, often resembling sunburn or eczema. Common offenders include tetracyclines, sulfonamides, and thiazide diuretics.
• Do Not Miss diagnoses:
  • Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN): These are life-threatening conditions characterized by widespread skin necrosis and detachment, often accompanied by mucosal involvement and systemic symptoms. They can be triggered by medications such as sulfonamides, penicillin, and NSAIDs.
  • Drug reaction with eosinophilia and systemic symptoms (DRESS): This is a rare but potentially life-threatening condition characterized by a rash, fever, lymphadenopathy, and internal organ involvement, often accompanied by eosinophilia. Common culprits include anticonvulsants, sulfonamides, and NSAIDs.
• Rare diagnoses:
  • Acute generalized exanthematous pustulosis (AGEP): This is a rare condition characterized by numerous small, sterile pustules on the skin, often accompanied by fever and systemic symptoms. It is usually triggered by medications such as beta-lactam antibiotics or macrolides.
  • Erythema multiforme: This is a rare condition characterized by target-like lesions on the skin, often accompanied by mucosal involvement and systemic symptoms. It can be triggered by medications such as sulfonamides, penicillin, and NSAIDs, as well as infections and other factors.