Subclinical autonomic nervous system dysfunction in compressive cervical myelopathy.

STUDY DESIGN

Laboratory evaluation of autonomic nervous system (ANS) in patients with cervical compressive myelopathy (CCM).

OBJECTIVE

To study the autonomic functions and heart rate variability (HRV) in patients with CCM and compare the findings after surgery.

SUMMARY OF BACKGROUND DATA

ANS dysfunction is well known after traumatic spinal cord injury. There are very few studies of ANS dysfunction in noncompressive myelopathy and there are no studies on compressive myelopathies.

METHODS

After excluding patients on cervical traction or with medical comorbidities, 29 adult patients with CCM were evaluated. Conventional autonomic function tests and HRV were studied in these patients. The same tests were done on 29 age- and sex-matched healthy controls. Student t test was used to find the significance of study parameters on continuous scale. Chi-square/Fisher exact test was used to find the significance of study parameters on categorical scale between two groups. Significance was assessed at 5% level.

RESULTS

Patients with CCM as compared with controls, showed significant difference in following parameters; deep breathing, Valsalva ratio, 30:15 (longest RR interval (duration between two consecutive R waves of ECG) around 30th second and the minimum RR interval around 15 seconds after standing up), and orthostatic fall of blood pressure. Except 30:15, there was no significant change of other autonomic function tests after surgery. Among the HRV parameters, there was a trend in increase in total power and decrease in root-mean-square differences of successive RR intervals; however, it did not reach statistical significance.

CONCLUSION

Patients with CCM have definite ANS dysfunction as compared to healthy age- and sex-matched controls. There is significant improvement in 30:15 ratio after surgery. HRV indices are also impaired and there is a trend for change in total power and root-mean-square differences of successive RR intervals suggesting loss of HRV.