In Reply We read with interest the letter to the editor by Fifel and DeBoer. Their comments focus on 3 published studies that shed light on circadian function in Parkinson disease (PD) and its possible link to frequently disrupted sleep-wake cycles in the PD population.
Videnovic et al1 studied 24-hour circadian secretion of melatonin in serum samples of 20 patients with PD taking dopaminergic therapy under modified constant-routine conditions. They found diminished amplitude of melatonin secretion in patients with PD and a strong correlation with excessive daytime sleepiness.1 No alterations in other circadian markers were found. Similarly, Breen et al2 reported significant reductions in melatonin levels in 30 patients with early-stage PD, along with increased cortisol levels and flattening of the circadian Bmal1 rhythm (one of the core clock genes). In contrast to these findings, Bolitho and colleagues3 found increased melatonin secretion and prolonged phase angle of entrainment in medicated patients with PD (n = 16) but not in unmedicated patients (n = 13) or matched control individuals (n = 28).
Videnovic A, Breen DP, Barker RA, Zee PC. The Central Clock in Patients With Parkinson Disease—Reply. JAMA Neurol. 2014;71(11):1456. doi:10.1001/jamaneurol.2014.2711