What causes steroid nerve flares with steroid injections?

Causes of Steroid Nerve Flares with Steroid Injections

Steroid nerve flares are primarily caused by crystal-induced inflammation from particulate steroids, mechanical trauma during needle insertion, and direct neurotoxic effects of certain steroid preparations, particularly when injected intrafascicularly. 1, 2

Mechanisms of Steroid Nerve Flares

• Crystal-induced inflammation: Particulate steroids can cause a transient inflammatory response when injected near nerve tissue, leading to increased pain 24-72 hours after injection 3

• Direct neurotoxicity: Intrafascicular injection of steroid preparations can cause direct toxic effects on peripheral nerve fibers, with varying degrees of damage depending on the specific steroid used 2

• Mechanical trauma: The needle itself can cause mechanical irritation or trauma to the nerve during injection, contributing to post-injection pain 4

• Chemical irritation: The acidic pH of standard steroid preparations may contribute to nerve irritation and post-injection pain, though neutralizing the pH has not been conclusively shown to reduce flare reactions 3

Incidence and Timing

• Approximately 33% of patients receiving extra-articular steroid injections experience a flare reaction, defined as an increase in pain after the initial injection 3

• Pain typically rebounds to pre-injection levels by day 1 after injection, followed by gradual improvement over the course of the first week 3

• Facial flushing, a systemic reaction to corticosteroid absorption, occurs in approximately 11% of patients receiving epidural steroid injections 5

Steroid-Specific Risk Factors

• Different steroid preparations carry varying risks of neurotoxicity 2:

  • Dexamethasone causes minimal damage to nerve tissue
  • Hydrocortisone and triamcinolone hexacetonide can cause widespread axonal and myelin degeneration when injected intrafascicularly

• Steroid-related adverse effects specifically reported with injections include 1:

  • Post-injection flare (following intra-articular use)
  • Pain exacerbation
  • Injection-site soreness

Anatomical Considerations

• Injection site is critical in determining risk of nerve injury - intrafascicular injection (directly into the nerve fascicle) causes significantly more damage than extrafascicular injection 2

• Transient sciatic nerve block has been reported following sacroiliac joint injections, possibly related to anterior capsular disruption and technique-related factors 4

• Nerve injury following steroid injection can range from mild and self-limiting to severe with poor response to conservative treatment 6

Prevention Strategies

• Use image guidance (fluoroscopy or ultrasound) to ensure accurate needle placement and avoid intrafascicular injection 4

• Consider using dexamethasone rather than more neurotoxic steroid preparations when injecting near nerve structures 2

• Be aware of anatomical variations and use proper technique to minimize risk of nerve injury 4

• Recognize that certain injection locations (such as the deltoid area) have higher risk of local tissue atrophy compared to others (like the gluteal area) 1

Serious Complications

• While rare, serious complications can occur, including:

  • Nerve injury requiring surgical intervention 6
  • Infection including meningitis, epidural abscess, or joint infection 7, 4
  • Spinal cord infarction, paraplegia, or quadriplegia (particularly with epidural administration) 1

• These serious complications emphasize the importance of proper technique, sterile conditions, and appropriate patient selection for steroid injections 7