Discography is a diagnostic test in which radiographic contrast is injected into the nucleus pulposus of the intervertebral disc. Although originally developed for the study of disc herniation, discography is now used most commonly to identify symptomatic disc degeneration. There are two components of discography: (1) the anatomic appearance of contrast spread within the disc (using plain radiographs and/or computed tomography [CT]) and (2) the presence or absence of typical pain during contrast injection within the disc (pain provocation).
Discography was first described by Lindblom in 1948. He used the technique to demonstrate disc ruptures and to determine if patients’ pain symptoms originated from the abnormal disc. Although the procedure was initially performed more than 60 years ago, discography still remains controversial largely because of validity concerns. In 1968, Holt (cited later) reported that discography was falsely positive in 37% of an asymptomatic population. However, much subsequent work supports the validity of provocative discography in identifying symptomatic disc abnormalities.
Identifying the specific pathology responsible for spinal pain is often difficult. This is particularly true given the high incidence of anatomic abnormalities in asymptomatic individuals and the presence of normal anatomy in some painful individuals, at least as demonstrated on conventional imaging studies.1,2 The primary purpose of diagnostic injections for chronic spinal pain is to identify which anatomic structure of the spine is causing pain and what the pathologic disorder is that affects it. Discography remains the only test available that attempts to correlate pain response from the patient during provocation with abnormal discs identified on imaging studies.
Whether or not it is important to make an anatomic diagnosis in patients with spinal pain is a matter of some debate.3,4 While some would argue that in the majority of patients, attempts at making an anatomic diagnosis are contraindicated, others feel that, at a minimum, making a diagnosis will help patients to heal by providing them with a clear understanding of their problem.5 The most important reason to make an anatomic diagnosis, however, is if there are treatments that can be directed toward specific pathology, leading to good outcomes. Many patients with spinal pain can be treated with interventional pain management procedures. The success of these procedures may depend on an accurate anatomic diagnosis; however, typically, little harm will come to the patient if the procedure fails. Traditionally, the indications for surgery have been felt to be neurologic loss. Increasingly, however, surgery is being performed for pain without neurologic loss, essentially becoming a pain management procedure. Although surgery may help some patients with chronic pain, the tissue injury that necessarily accompanies surgery may potentially lead to devastating consequences. If surgery is being considered for patients with chronic pain, an accurate diagnosis is essential. In this chapter, we focus on the role of diagnostic injections in presurgical decision making.