Steroid-Induced Sleep Disturbance and Delirium: A Focused Review for Critically Ill Patients

Steroid receptors are densely located in behavior centers in the brain: the amygdala, septum, and hippocampus. Pharmacologic changes in gene expression alter norepinephrine and serotonin levels in the brain as well as their receptors.³² Prolonged exposure to exogenous steroids has been shown to decrease amygdala and hippocampal volumes.^34,35 Furthermore, prolonged corticosteroid exposure has been shown to decrease the number of steroid receptors in the hippocampus, pituitary gland, and amygdala.³⁶ In a somewhat paradoxical finding, the production of CNS proinflammatory cytokines like interleuken-1β and tumor necrosis factor α has been seen after steroid administration, suggesting alternate gene signaling in the CNS.³⁷ Although not proven conclusively, it is felt that these physiologic changes and hyperactivity of the HPA axis are predominantly responsible for changes in behavior, mood, memory, and eventually psychosis in steroid-treated patients.^33,38

Finally, alterations in cognition and behavior may be related to steroid-induced changes in CNS carbohydrate, protein, and lipid metabolism with subsequent cellular neurotoxicity.^32,38 Glucose uptake into the hippocampus is decreased with steroid exposure. Additionally, breakdown of metabolic compounds to produce energy can be destructive if left unchecked for prolonged periods. DHEA, growth hormone, and testosterone work to repair catabolic damage produced by cortisol, known as anabolic balance. A low anabolic balance (low DHEA levels to high cortisol levels) leads to a cascade of dysregulation in brain activity.³⁹

Changes in Natural Sleep-Wake Cycles

Natural sleep pathways are also affected by steroids. The sleep-wake cycle is primarily regulated in the hypothalamus with circadian release of melatonin from the pineal gland. Melatonin release is highest at night, where it promotes sleep onset and continuity. Upstream, tryptophan is an amino acid that serves as a precursor to serotonin and melatonin.⁴⁰ Both endogenous and exogenous corticosteroids decrease serum melatonin levels with a markedly diminished circadian rhythm secretion.^41,42Demish and colleagues found a significant decrease in mean (SD) nocturnal melatonin plasma levels after the evening administration of oral dexamethasone 1 mg in 11 healthy volunteers: 127 (42) pg/mL before vs 73 (38) pg/mL after; P < .01.⁴² This result is likely due to decreased cellular metabolism and melatonin synthesis in the pineal gland. Of note, melatonin has neuroprotective affects, and the administration of melatonin has been shown to reverse some steroid-induced neurotoxicities in animal models.⁴³

Steroids also reduce the uptake of tryptophan into the brain.³³ Additionally, in animal models, dexamethasone administration caused a significant decrease in the gene expression of tryptophan hydroxylase, which is part of the multistep pathway in synthesizing serotonin from L-tryptophan. These effects upstream could inhibit the biosynthetic capacity of both melatonin and serotonin.⁴⁴

A third pathway investigated in sleep regulation are the orexin neuropeptides. Orexins are produced in the hypothalamus and stimulate daytime wake activity in monoaminergic and cholinergic neurons. Subsequently, orexin receptor antagonists are a newer class of drugs aimed at mitigating nighttime hyperarousal and sleep disruption. Orexin overexpression may be a causal factor in steroid-induced sleep disturbance. However, this effect was specifically evaluated in a recent study in children with acute lymphoblastic leukemia, which showed that cerebral spinal fluid orexin levels (SD) were not significantly different from baseline after dexamethasone administration: 574 (26.6) pg/mL vs 580 (126.1) pg/mL; P = .8.⁴⁵