Post-Radiofrequency Ablation Neuritis of the Spine

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Radiofrequency ablation (RFA), also referred to as radiofrequency neurotomy or radiofrequency rhizotomy, is a minimally invasive interventional procedure that employs thermal energy to denervate specific neural pathways implicated in chronic pain signaling. The fundamental principle involves the delivery of a high-frequency alternating current through a specialized electrode needle precisely positioned near the target nerve. This current generates ionic agitation within the adjacent tissue, leading to frictional heating and the creation of a controlled thermal lesion. The objective of this targeted tissue destruction, typically via coagulative necrosis, is to interrupt the afferent transmission of nociceptive signals from the periphery to the central nervous system, thereby providing pain relief. The temperature at the electrode tip is carefully monitored and controlled, usually reaching 80−90∘C in conventional thermal RFA, to create a predictable lesion size while minimizing injury to non-target tissues.

The subsequent inflammatory and regenerative responses of the nerve can, paradoxically, lead to new or altered pain states, a phenomenon central to the understanding of post-RFA neuritis. An important aspect of post-RFA care is the differentiation between a transient post-procedural discomfort and the development of a true persistent post-RFA neuritis. True neuritis is characterised by its persistence, severity, and distinct neuropathic quality (e.g., intense burning, shooting pain, dysaesthesia).

Pathophysiology

The development of post-RFA neuritis is multifactorial, with several proposed pathophysiological mechanisms stemming from the nerve injury induced by the procedure.

Direct Thermal Nerve Injury, Axonal Degeneration (Wallerian), and Inflammatory Sequelae

Thermal RFA intentionally causes nerve degeneration (Wallerian), which, along with the subsequent inflammation, can paradoxically trigger neuropathic pain. Even less destructive pulsed RFA can cause sufficient neural irritation to induce neuritis..

Consequences of Incomplete or Partial Nerve Ablation

If the nerve isn't fully ablated, partially damaged, hyperexcitable axons can become a source of persistent neuropathic pain, underscoring the need for procedural precision.

Aberrant Nerve Regeneration, Neuroma Formation, and Deafferentation Pain

Faulty nerve regeneration post-injury can lead to painful neuroma formation (disorganized nerve tissue). Alternatively, the loss of sensory input can cause deafferentation pain due to maladaptive changes in the central nervous system.

Injury to Adjacent or Variant Neural Structures

Unintentional thermal damage to nearby nerves or unanticipated anatomical variants may also trigger neuritis.

Epidemiology

Cervical Spine

The third occipital nerve (branch of C3) requires special attention, firstly because it is one of the more commonly ablated nerves (for cervicogenic headache), and secondly because it provides sensory innervation to the skin overlying the suboccipital region. The latter point is likely why neuritis is more common here. Neuritis or neuralgia following RFA of the TON is a notably common adverse event, with reported incidences that are generally higher than those seen with RFA at other spinal levels. Several studies have attempted to quantify this risk, with incidence ranging from 19 to 55%:

• A study by Gazelka et al retrospectively reviewed 64 patients who underwent RFA of the nerves supplying the C2-C3 facet joint or specifically the TON. They found that 12 of these patients (19%) developed new neuropathic pain consistent with third occipital neuralgia, characterized by symptoms such as burning, tingling, numbness, or painful dysesthesia in the TON distribution. Amongst these 12, symptoms persisted for an average of 2.6 months (range 1 to 6 months) in 7 patients. One patient still had neuritis at one year, and four were lost to follow up. 10 of the 12 required intervention for neuritis pain.
• A study by Govind et al., reported dysesthesias in the cutaneous distribution of the TON in 55% of procedures (9.2% per lesion), but typically lasted only 7-10 days and none were distressing enough to require intervention.
• Another study investigating repeat TON RFA for recurrent cervicogenic headaches or occipital neuralgia found that 41% of patients (9 out of 22) experienced neurogenic side effects (itching, numbness, hyperaesthesia, paraesthesia, numbness). However 95% would repeat the procedure again if their original pain returned.

Patients who develop neuritis or neuralgia following TON RFA typically present with a new onset of neuropathic symptoms localized to the cutaneous distribution of the TON, which is the suboccipital area, sometimes extending towards the vertex or retroauricular region.

A notable, though usually transient, complication specifically associated with TON RFA is ataxia, which is almost universal immediately post procedure. Patients may experience dysequilibrium or unsteadiness, which typically resolves within 30 minutes to a few hours post-procedure. The occurrence of ataxia suggests that the RFA lesion may affect proprioceptive fibers from the upper cervical joints or muscles, or that the TON itself has an unappreciated role in head-neck position sense, the disruption of which leads to transient balance disturbance.

Lumbar Spine

Neuritis is generally uncommon:

• A study by Singh et al. (2019) involving a retrospective evaluation of patients undergoing lumbar RFN found that the incidence of PNN was 6.4% (5 out of 77) in a group that received corticosteroids post-RFA and 6.9% (6 out of 87) in a group that did not, with no statistically significant difference between the groups. These figures suggest an overall incidence in the range of 6-7%.
• A retrospective analysis by Kornick et al. (2004), involving 616 radiofrequency lesions, reported that paresthesia occurred in 1.0% of ablations. Of these cases, three involved neuritic pain lasting less than 2 weeks, and three were characterized by localized pain lasting more than 2 weeks.

Risk Factors

• Nerve includes sensory supply to the skin (expected or anatomical variant)
• Female
• Diabetes
• Migraine
• Pain "plus"

Clinical Presentation

The clinical presentation of post-RFA neuritis is characterized by the new onset of pain and/or sensory disturbances that are temporally related to the RFA procedure and localized to the anatomical area of the ablated nerve or its cutaneous distribution.

Patients often report abnormal sensations such as a "sunburnt" feeling, persistent burning, tingling (paraesthesia), numbness, or painful, abnormal sensations (dysaesthesia) in response to normally non-painful stimuli (allodynia) or an exaggerated response to painful stimuli (hyperalgesia). These symptoms are qualitatively different from the immediate, expected post-procedural soreness, which is generally mild, nociceptive in nature, and resolves relatively quickly.

The onset of symptoms can vary, typically occurring within a few days to several weeks after the RFA procedure. Some patients may experience symptoms almost immediately after the local anesthetic from the procedure wears off, while in others, the onset may be more delayed. This variability in onset may reflect different underlying pathophysiological timelines, such as acute inflammation versus the more delayed processes of Wallerian degeneration or early aberrant regeneration.

Diagnosis

The diagnosis of post RFA neuritis is primarily clinical. It relies heavily on a careful history focusing on the new onset of characteristic neuropathic symptoms in the appropriate anatomical distribution following the RFA procedure. Sensory testing may reveal hyperesthesia, allodynia, or hypoesthesia in the nerve territory.

The main diagnostic challenge lies in distinguishing these neuritic symptoms from:

1. Typical post-procedural soreness: Which is usually nociceptive, milder, and resolves within a few days.
2. Ineffective RFA: Where the patient's original pain persists or returns quickly, without the new qualitative features of neuropathic pain. The subjective nature of the symptoms (pain, dysesthesia) and the potential overlap with expected, transient post-procedural sensations (e.g., minor numbness or burning at the lesion site) can make immediate differentiation difficult. A high index of suspicion, meticulous attention to the timing of onset, the specific neuropathic quality of the pain, and its precise anatomical distribution are critical for an accurate diagnosis

Prognosis

The prognosis and natural history of neuritis following TON RFA exhibit considerable variability, contributing to challenges in patient counseling and management planning. Some reports suggest that certain sensory disturbances, such as dysesthesias, can be relatively mild and self-limiting lasting only a few days, while variably it may last for months or rarely even longer.