[Drug hypersensitivity: When systemic symptoms and pustules converge]

Area of Science:

• Dermatology
• Pharmacology
• Clinical Medicine

Background:

• Severe cutaneous adverse drug reactions (SCARs) are defined by fulfilling criteria for multiple drug-associated reactions.
• Overlapping SCARs present diagnostic challenges due to shared clinical manifestations.
• This report details a rare case of an overlapping SCAR.

Purpose of the Study:

• To present a case of an overlapping severe cutaneous adverse drug reaction.
• To illustrate the diagnostic difficulties associated with overlapping SCARs.
• To discuss the clinical presentation and management of a patient with phenytoin-induced overlapping SCAR.

Main Methods:

• A 53-year-old female patient with diabetes and hypertension was treated with metformin, linagliptin, and nifedipine.
• Phenytoin was initiated for a seizure, leading to erythema, pruritus, and fever 5 weeks later.
• Diagnostic evaluation included clinical examination, laboratory tests (leukocytosis, eosinophilia, acute kidney injury), and skin biopsy (interface dermatitis, perivasculitis, eosinophilia).
• RegiSCAR and EuroSCAR scoring systems were used to assess the severity and overlap of the reaction.

Main Results:

• The patient developed generalized polymorphic skin lesions, including maculopapular and bullous eruptions, along with facial pustules.
• Laboratory findings revealed leukocytosis with neutrophilia, significant eosinophilia, and acute kidney injury.
• Skin biopsy indicated chronic interface dermatitis, superficial perivasculitis, and eosinophilic infiltration.
• The patient's condition was classified as a probable overlapping SCAR based on RegiSCAR (4 points) and EuroSCAR (6 points) scores.
• Initial treatment with antihistamines was ineffective; subsequent steroid therapy with methylprednisolone and prednisone was initiated.

Conclusions:

• The patient's reaction, occurring 5 weeks after phenytoin initiation, met criteria for an overlapping SCAR.
• Confirmed cases of overlapping SCARs are rare due to diagnostic ambiguities.
• Early identification of SCARs can be challenging in the acute phase due to overlapping clinical features, necessitating careful evaluation and scoring.