sQUIZ your knowledge! Progressive thickening and hardening of the skin on the upper back

Jingru Sun¹, Shengguo Yi², Ping Tu¹

• ¹Department of Dermatology and Venereology, Peking University First Hospital, Beijing 100034, China, Beijing Key Laboratory of Molecular Diagnosis on Dermatoses, Beijing 100034, China, National Clinical Research Center for Skin and Immune Diseases, Beijing 100034, China.+1