NEFL and peripheral nervous system disorder: In particular, injury might be occurring in the peripheral nervous system, which would help explain the association between COVID-19 and peripheral nerve disorders and myopathy.7 Consistent with this possibility are the observations, in COVID-19 patients, of a raised NfL level associated with critical illness polyneuropathy/myopathy31 (for which duration of admission is an established risk factor32) and of a raised serum NfL level in the absence of raised levels of NfL in theCSF.17