Background and Objectives : The aim of this study was to assess the disease trajectory and recurrence rate of pemphigus based on the analysis of the gap time between successive recurrent events. In this regard, the most important associated factors with the risk of recurrence could be explained.

  Methods: This longitudinal study was performed on 112 pemphigus patients who attended the dermatology department of Imam Khomeini Hospital, Tehran, Iran, from March 2006 to January 2013. The study duration was considered from the diagnosis of the disease to December 2013. Recurrent events were analyzed based on the gap time between successive events using the multivariate time dependent frailty model. The time between two recurrent gap times was determined monthly between two successive events.

  Results : Decreasing the gap times between two successive events indicates that the subsequent event after the first recurrence occurs with shorter time intervals. So, the disease trajectory represents an increase in the recurrence rate over time. Based on the results of multivariate frailty model, IgG antibody's level was the only effective factor on the recurrence hazard rate of the patients. Also, this model proved that the frailty effects were time dependent frailties.

  Conclusion: Assessing the disease trajectory and recurrence hazard rate can be achieved through analyzing the gap time between successive recurrent events. This analysis also identifies the factors that influence the risk of subsequent recurrent events.