The effect of epidural methylprednisolone acetate injection on the hypothalamic-pituitary-adrenal axis.

STUDY OBJECTIVE

To evaluate the effect of an epidural corticosteroid injection of 80 mg and 40 mg of methylprednisolone acetate on the hypothalamic-pituitary-adrenal axis and on back pain.

DESIGN

Randomized, single-blinded prospective study.

SETTING

Operating room of a university-affiliated hospital.

PATIENTS

42 patients with low back pain due to radiculopathy.

INTERVENTIONS

Group 1 received an epidural corticosteroid injection of 80 mg of methylprednisolone acetate, and Group 2 received an epidural corticosteroid injection of 40 mg of methylprednisolone acetate. All study patients underwent a stimulation test of one μg of adrenocorticotropin hormone (ACTH), and their pain levels were graded just prior to and following the epidural corticosteroid injection on weeks one, 3, and 4.

MEASUREMENTS

Serum cortisol of the ACTH stimulation tests and back pain levels were rated using a visual analog scale (VAS). Serum cortisol levels lower than 18 ng/mL 30 minutes following the ACTH stimulation test were considered to be secondary adrenal insufficiency.

MAIN RESULTS

21 patients were enrolled in each group. The rate of secondary adrenal insufficiency in Group 1 was ~86%, ~ 22%, and ~17% of patients versus ~53% (P = 0.024), 15% (P = 0.874), and ~12% (P = 0.715) of Group 2 patients at weeks one, 3, and 4, respectively. About 62%, 56%, and 39% of Group 1 patients had a favorable clinical response as opposed to ~47% (P = 0362), 35% (P = 0.21), and ~6% (P = 0.049) of Group 2 patients at weeks one, 3, and 4, respectively.

CONCLUSIONS

Epidural corticosteroid injection of methylprednisolone acetate in both groups was associated with very high rates of secondary adrenal insufficiency, but significantly more so in Group 1 at week one. This suppression was transient, with recovery of the gland in most patients noted over the ensuing weeks. An epidural corticosteroid injection of 80 mg had higher rates of favorable clinical response than a 40 mg injection, but significantly more so at week 4 only. This favorable response waned over a few weeks in both groups.