Which of the following is the least common complication of measles?

Among the given options, though all are complications of measles. most rare one is Sub-acute Sclerosing Pan Encephalitis; while the other three are common complications. SSPE usually occurs after many years of initial infection. It is characterised by progressive mental deterioration and paralysis. It is diagnosed by the high levels of complement fixing antibodies in the serum and cerebrospinal fluid. Ref: Park's Textbook of Preventive and Social Medicine 19th edition; pages 126 - 129 ; Measles By Maxine Rosaler; pages 10 - 11 ; Infections of the Central Nervous System By W. Michael Scheld, Richard J. Whitley, Christina M. Marra; pages 112