Which finding in a patient taking lamotrigine requires immediate follow-up?

Skin blistering in a patient taking lamotrigine is a finding that requires immediate follow-up because it may indicate a serious side effect known as Stevens-Johnson syndrome (SJS) or toxic epidermal necrolysis (TEN). These conditions are potentially life-threatening skin reactions characterized by extensive skin damage and can lead to severe complications, including infections and systemic involvement. Lamotrigine is associated with these severe adverse reactions, especially when the dosage is increased too rapidly or if the patient is also taking other medications that can increase the risk of rash.

In contrast, abnormal dreams, dyspepsia, and xerostomia, while they can be bothersome or affect quality of life, do not carry the same immediate life-threatening risk as skin blistering. These symptoms may warrant attention and management, but they are generally not urgent and do not necessitate the same level of immediate medical intervention as the severe skin reactions. Thus, skin blistering stands out as the critical finding that demands prompt assessment and intervention.