The Role of Genetic Testing in the Differential Diagnosis of Pustular Dermatoses: A Pediatric Case of Generalized Pustular Psoriasis Associated with the IL36RN Variant

General pustular psoriasis (GPP) is a rare, potentially life-threatening neutrophilic dermatosis. Pediatric cases are uncommon and often misdiagnosed due to overlapping clinical and histopathological features with other pustular dermatoses. We present a case of an 11-year-old boy, initially diagnosed with Sneddon–Wilkinson syndrome, who presented with disseminated pustular eruptions, with no response to antibiotics, dapsone, and glucocorticosteroids. In histopathology, we observed subcorneal neutrophilic pustules. Due to atypical features and poor treatment response, the patient underwent genetic testing, which revealed a homozygous IL36RN gene c.338C>T (p.Ser113Leu) pathogenic variant, which enabled a definitive diagnosis of GPP. Treatment with acitretin led to clinical improvement. Pediatric GPP poses diagnostic and treatment challenges. Genetic testing for IL36RN pathogenic variants may aid in the diagnosis, especially in atypical cases. The presence of the biallelic IL36RN pathogenic variant supports the diagnosis of DITRA (Deficiency of the IL-36 Receptor Antagonist, ORPHA:404546)—a monogenic autoinflammatory form of GPP.