Diagnostic selective nerve root blocks: indications and usefulness.

Diagnostic SNRIs are a useful tool in the diagnosis of radicular pain in atypical presentations. Diagnostic SNRI is indicated in the following circumstances: (1) for atypical extremity pain; (2) when imaging studies and clinical presentation do not correlate; (3) when electromyography and MRI are not corroborative or are equivocal; (4) for anomalous innervations, such [figure: see text] as conjoint nerve roots or furcal nerves [71]; (5) for failed back surgery syndrome with atypical extremity pain; and (6) for transitional vertebrae. Patients should have demonstrated a failure to improve with less invasive treatment. In these patients, a diagnostic SNRI may localize the pain to a specific spinal nerve. It must be emphasized that the diagnostic SNRI only determines if pain is emanating from a specific nerve root or spinal nerve. A diagnostic SNRI does not determine what has caused the nerve root or spinal nerve pain, nor does it provide prognostic information. The etiology of the nerve root pain, mechanism of injury, underlying anatomy, duration of symptoms, comorbidities, patient desire, physician skill, and a host of other factors determine the appropriate treatment and prognosis.