What is a notable clinical presentation in a patient suspected of Stevens-Johnson syndrome after starting allopurinol?

In patients suspected of Stevens-Johnson syndrome (SJS) following the initiation of allopurinol, the notable clinical presentation involves a phenomenon where pressure applied laterally to the lesion can cause extension of the injury. This is known as the Nikolsky sign, which is associated with conditions that cause blistering or desquamation of the skin.

Stevens-Johnson syndrome is a severe form of mucocutaneous reaction usually triggered by medications. It causes widespread necrosis and sloughing of the skin and mucous membranes. The presence of the Nikolsky sign indicates the skin's poor integrity, making it more susceptible to damage and further separation under mechanical stress. This characteristic is particularly important because it helps differentiate SJS from other dermatological conditions that may not exhibit this sign.

Other presentations such as pitting edema, formation of bullae, and dermatitis with weeping lesions can occur in various skin conditions but are not specifically characteristic of SJS in relation to allopurinol. Therefore, recognizing the lateral pressure extension as a notable clinical presentation is crucial for diagnosing and managing Stevens-Johnson syndrome effectively.