PTH and Marchiafava-Bignami disease: Although optimal PTH levels for patients with CKD stage G3a to G5 are not clearly defined, the potential adverse consequences of prolonged PTH elevations are reflected by the fact that the Kidney Disease: Improving Global Outcomes (KDIGO) CKD-mineral and bone disorder (CKD-MBD) guidelines recommend regular monitoring of PTH levels starting in CKD stage G3a, in order to identify patients with progressively rising or persistently elevated PTH levels above the upper limit of normal, so that at-risk individuals can be recognised and evaluated for modifiable risk factors [7].