Carpal tunnel syndrome affects the median nerve in the wrist, causing discomfort and other symptoms. Many individuals notice their symptoms worsen at night. This is influenced by several physiological and behavioral factors that increase pressure on the median nerve during rest, often disrupting sleep.
Understanding Carpal Tunnel Syndrome
The carpal tunnel is a narrow passageway on the palm side of the wrist, formed by bones and a strong ligament. Through this space, nine tendons and the median nerve pass. This nerve provides sensation to the thumb, index, middle, and half of the ring finger, and controls some thumb muscles. When compressed, typical symptoms include numbness, tingling, and pain in the affected fingers. This compression can also lead to hand weakness, making gripping difficult.
Impact of Sleeping Positions
Sleeping postures significantly contribute to worsened carpal tunnel symptoms at night. Many people sleep with their wrists bent or extended for prolonged periods. These positions, such as wrists flexed inward or tucked under the body, increase pressure within the carpal tunnel. For instance, curling up in a fetal position or stomach sleeping with hands under the head can heighten nerve compression, as even slight wrist flexion (as little as 20 degrees) can alter symptoms. This increased pressure irritates the median nerve, causing numbness, tingling, and pain that often wake individuals from sleep.
Fluid Accumulation and Reduced Movement
Fluid accumulation and reduced movement during sleep also play a role in nighttime symptom exacerbation. When lying down, gravitational forces that drain fluids from the extremities are minimized, leading to increased fluid accumulation (edema) in the hands and wrists. This further compresses the median nerve within the carpal tunnel; conditions like pregnancy can make this more noticeable. The lack of movement during sleep means muscles and joints do not actively circulate blood and tissue fluids, unlike during waking hours when hand and wrist movements help maintain fluid balance. Without this active movement, fluid builds up in the carpal tunnel area, contributing to increased nerve pressure and intensifying symptoms.
Circadian Rhythms and Pain Perception
Circadian rhythms and altered pain perception at night also influence carpal tunnel symptom severity. Pain thresholds often become lower at night, a fluctuation partly influenced by hormonal changes like decreased cortisol levels in the evening. Cortisol, an anti-inflammatory hormone, has a reduced presence that can increase inflammation susceptibility. The absence of daytime distractions also makes individuals more aware of their physical discomfort. At night, with fewer external stimuli, pain may be perceived as more severe, and this heightened awareness combined with biological rhythms that lower pain tolerance contributes to worsened symptoms.