Manenschijn L, Koper JW, van den Akker ELT, de Heide LJM, Geerdink EAM, de Jong FH, Feelders RA, van Rossum EFC. A Novel Tool in the Diagnosis and Follow-Up of (Cyclic) Cushing's Syndrome: Measurement of Long-Term Cortisol in Scalp Hair. The Journal of Clinical Endocrinology & Metabolism. 2012 Oct;97(10):E1836–43. doi: 10.1210/jc.2012-1852.