Mortality of Bullous Pemphigoid in China

We read with interest the study by Li et al1 describing the prognosis of Bullous Pemphigoid (BP) in a large patient cohort in China. The authors report a first year mortality rate significantly lower than those reported in previous European studies. We recently conducted a similar retrospective study in our institution with a cohort of 101 BP patients and also found a first year mortality rate of 12.9%.2 However, after reading the results section, it strikes me that the authors do not provide information about how many patients had a follow-up time of at least 2 years and how many patients had a follow-up time of at least 5 years. As mentioned, the median follow-up time was 3 years. Regarding to this data and in the best scenario, the number of patients with a follow-up time of 5 years or longer would have been of 70. Consequently, 1-year mortality rate would have been calculated from a cohort of 140 patients and 5-year mortality rate would have been estimated from a cohort of 70 patients. Moreover, an indeterminate proportion of the patients lost to follow up from the first to the fifth year after diagnosis could have died. As a result, 5-year mortality would have been significantly higher. In our opinion, the 1-year and 5-year mortality rates are not comparable. Furthermore, the observed 5-year mortality rate is not very reliable. References1. Li J, Zuo YG, Zheng HY. Mortality of Bullous Pemphigoid in China. JAMA Dermatol. 2013; 149(1):106-8.2. Gual A, Mascaró JM Jr, Rojas-Farreras S et al. Mortality of Bullous Pemphigoid in the first year after diagnosis: a retrospective study in a Spanish medical centre. J Eur Acad Dermatol Venereol. 2012; Dec 22. doi: 10.1111/jdv.12065. [Epub ahead of print]