Functional brown adipose tissue and sympathetic activity after cold exposure in humans with type 1 narcolepsy.

STUDY OBJECTIVES

To investigate the activity of brown adipose tissue (BAT) in patients with type 1 narcolepsy during cold exposure using two separate scans of sympathetic and metabolic activity of BAT to evaluate whether orexin deficiency leads to altered nonshivering thermoregulation in narcolepsy.

METHODS

Seven patients with type 1 narcolepsy and seven healthy controls underwent two consecutive scans after 2 hr cold exposure: 123I-meta-iodo-benzyl-guanidine (123I-MIBG) single photon emission computed tomography and18F-2-deoxy-glucose (18F-FDG) positron emission tomography and computed tomography to visualize sympathetic innervation and metabolic activity of BAT, respectively. Plasma levels of eight hormones regulating BAT activity were measured before and after 2 hr in the cold.

RESULTS

18F-FDG-uptake and uptake of 123I-MIBG in BAT after 2 hr cold exposure were observed in all individuals, but the activity of BAT was not significantly different between patients with type 1 narcolepsy and healthy controls (p > 0.05). Plasma levels of GLP-1 were higher in patients with type 1 narcolepsy compared with controls (p < 0.05), but not altered by cold adaptation in patients and controls (p > 0.05). FGF21 concentrations decreased after 2 hr cold exposure in both patients with type 1 narcolepsy and healthy participants (p < 0.05).

CONCLUSIONS

Sympathetic and metabolic activity of BAT was observed after cold exposure in patients with type 1 narcolepsy. Increased GLP-1 in narcolepsy may suggest autonomic dysfunction with metabolic changes. We conclude that BAT is functional after cold exposure in spite of the loss of orexinergic neurons in narcolepsy.