Area under the curve: a metric for patient subjective responses in episodic diseases

Herpes zoster manifests as a characteristic painful rash that resolves within 2 months of initial presentation in 90% of patients. As pain is a hallmark of the disease, the severity of an episode can be described by the magnitude and duration of pain. The Brief Pain Inventory (BPI) was used to follow the daily and weekly amount of pain reported by 50 patients with herpes zoster. Results demonstrate that the BPI is a reproducible, responsive and valid measure of pain due to herpes zoster. From the individual responses on the BPI, the area under the curve (AUC) for each patient was derived from the pain reported on sequential administrations of the BPI. This metric was simple to calculate, easy to explain and captured two dimensions of this episodic disease (magnitude and duration of pain) in a single continuous measure. AUC could prove useful in the application of patient response data to intervention trials in diseases that are of an episodic nature.