Background: Epidural steroid injections (ESI) are therapeutically useful for the treatment of herniated intervertebral discs and spinal stenosis. However, there is a lack of evidence-based data about the safety of steroids.
Objectives: The aim of this study was to determine the period of hypothalamus-pituitary-adrenal (HPA) axis suppression by salivary cortisol measurements after a single epidural injection of 40 mg of triamcinolone.
Study design: Clinical observational pilot study.
Setting: Outpatient follow-up.
Methods: In this study, 8 patients with lumbar intervertebral disc herniation or spinal stenosis were enrolled. All patients had received ESI (triamcinolone 40 mg) under C-arm guidance. Salivary cortisol concentrations were assessed between 8:00 am and 9:00 am; both before and after ESI (Day 0 [the day prior to injection], 1, 3, 5, 7, 14, 21, 28). Additionally, body weight, blood pressure, 0-10 numeric rating scale (NRS), and fasting blood sugar levels were evaluated.
Results: HPA axis suppression was observed in all patients for 19.9 ± 6.8 days after ESI (salivary cortisol < 0.1 ug/mL). In total, 5 of 8 patients reached baseline salivary cortisol concentrations within the clinical trial period. The time taken to reach baseline concentrations after ESI was 19.4 ± 8.3 days. The period of HPA axis suppression was not correlated with baseline salivary cortisol concentrations, and NRS scores.
Limitations: Adrenal insufficiency cannot be confirmed by simple salivary cortisol measurements. Furthermore, the period studied was too short for all patients' HPA axis function to reach the baseline value. Finally, the study design does not allow for the confounding effects of pain and stress on cortisol levels.
Conclusions: HPA axis function was suppressed after ESI until Day 21 and returned to the normal range after 19.9 ± 6.8 days. Therefore, we suggest that the minimal interval between ESI treatments should be at least one month. In addition, we report that salivary cortisol measurements are very useful diagnostic predictors of HPA function.