Differential Diagnosis for Diffuse Body Rash with Erythematous Lips and Elevated CRP
Single Most Likely Diagnosis
- Stevens-Johnson Syndrome (SJS)/Toxic Epidermal Necrolysis (TEN): Given the recent initiation of lamotrigine, a known culprit drug for SJS/TEN, and the presentation of a diffuse body rash along with erythematous lips, this diagnosis is highly plausible. The elevated CRP suggests an inflammatory response, which is consistent with SJS/TEN.
Other Likely Diagnoses
- Drug Rash with Eosinophilia and Systemic Symptoms (DRESS): This condition is also associated with the use of lamotrigine and can present with a diffuse rash, fever, lymphadenopathy, and elevated inflammatory markers like CRP. The timeline of starting lamotrigine 3 weeks ago fits with the typical onset of DRESS.
- Allergic Contact Dermatitis: Although less likely given the systemic symptoms and the elevated CRP, an allergic reaction to a new medication like lamotrigine could potentially cause a widespread rash. However, the involvement of erythematous lips and systemic inflammation makes this less probable.
Do Not Miss Diagnoses
- Severe Sepsis: Although the presentation does not strongly suggest sepsis, any patient with a rash and elevated inflammatory markers should be evaluated for infection, especially if there are signs of systemic illness. Missing sepsis could be fatal.
- Autoimmune Disorders (e.g., Lupus, Rheumatoid Arthritis): These conditions can present with rashes and elevated CRP. While less likely given the temporal association with lamotrigine, they are critical to consider due to their potential for serious morbidity if not treated.
Rare Diagnoses
- Erythema Multiforme: A skin condition characterized by target lesions, which can be triggered by medications and infections. It's less likely given the description of a diffuse rash but should be considered, especially if the rash has specific targetoid lesions.
- Acute Generalized Exanthematous Pustulosis (AGEP): A rare condition characterized by numerous small, sterile pustules on a background of erythema, often associated with drug use. It's a rare side effect of medications but could be considered in the differential diagnosis of a patient with a new drug exposure and a rash.