Selective Nerve Root Blocks: Results - Part B

Results Continued ...

A related utility of selective nerve root blocks is their negative predictive value. The question that arises is: in patients with a positive response to selective nerve root blocks, will surgery relieve their pain? This question has not been addressed using only the immediate, diagnostic response to local anaesthetics; but it has been answered by considering the prolonged response attributed to steroids.

One study examined the surgical outcome of 71 patients who obtained greater than 80% immediate relief of their radicular pain following a diagnostic selective nerve root block (16). What was correlated subsequently was the outcome of surgical therapy versus the degree of pain relief at one week following the block - referred to as the 'steroid response' (16).

It emerged that, overall, the 'steroid response' offered limited sensitivity but attractive positive and negative predictive values for surgical outcome (Table 1). Furthermore, it emerged that this test was of limited value in patients with symptoms of less than 1 year's duration (Table 2) but had good negative predictive power in patients with longer durations of symptoms (Table 3). In short, patients who fail to obtain sustained relief of radicular pain (relief attributed by inference to the use of steroids) are unlikely to benefit from surgery.

Table 1. Correlation between surgical outcome and steroid response in 71 patients who underwent selective nerve root blocks (16).

Table 2. Correlation between surgical outcome and steroid response in 20 patients with leg pain lasting less than 1 year who underwent selective nerve root blocks (16).

Table 3. Correlation between surgical outcome and steroid response in 51 patients with leg pain lasting longer than 1 year who underwent selective nerve root blocks.

Thus, whatever theoretical or axiomatic attraction selective nerve root blocks might have as a diagnostic test to determine whether or not a given root is symptomatic, their further utility is that if corticosteroids are administered in addition to local anaesthetic, they can predict if a patient will not respond to surgery. Using blocks in this way may or may not improve therapeutic outcome but can significantly curtail unnecessary and futile major surgery.