Assessing the Autoantibody levels in Relation to Recurrence of Pemphigus: Joint Modeling of Longitudinal Measurements and Recurrent Event Times

BACKGROUND Pemphigus is an autoimmune bullous disease and it is unclear what triggers and deteriorates it. The current study aimed to evaluate whether increasing the IgG antibody titer represents a good indicator of the pemphigus recurrence. OBJECTIVES The current study aimed to evaluate whether increasing IgG titer is an indicator of the expected recurrence. PATIENTS AND METHODS The current study was conducted at the Department of Dermatology, Imam Khomeini Hospital, Tehran University of Medical Sciences, between March 2007 and December 2012. A total of 112 patients with confirmed diagnosis of pemphigus based on clinical, histological and immuno-histological criteria were engaged in the study. The primary outcomes of the study were recurrent event times and IgG (Immunoglobulin G) antibody titer at each attendance. Joint model with shared random-effects was applied to assess the association between the two processes and investigate the affective factors. RESULTS Up to 8 recurrences were observed during the study time, but only 10% of the patients experienced more than 5 recurrences. A significant linear increasing trend in IgG antibody titer over time was found, IgG antibody titer increased 2.43% each month (P < 0.0001). The results showed positive correlation between IgG antibody titer and recurrence of pemphigus (P < 0.0001). CONCLUSIONS The patients with higher IgG antibody titer were more likely to experience pemphigus recurrence. Therefore it can be concluded that titer of IgG and its increase may provide information regarding the progression of the pemphigus and the hazard of its recurrence.