Insights into Fluoroscopy-guided Techniques, Thoracic Disc Herniation Treatment, and Genetic Testing of Patients on Chronic Opioid Therapy Presented at ASIPP 2012

These studies were among those selected for special recognition at the 2012 annual meeting of the American Society of Interventional Pain Physicians (ASIPP).

Imaging Technique May Not Always Prevent Intravascular Injection during Interventional Procedures

Chang, Candido, and Knezevic wrote that the fluoroscopy technique known as digital subtraction angiography (DSA) may help “minimize complications from interventional neuraxial procedures where it is imperative to identify vascular compromise during the injection.” However, use of this procedure may not eliminate risk of severe adverse events, as illustrated in the case study presented by the authors. In the case study, an 80-year-old man with severe lumbar spinal stenosis and chronic L5 radicular pain who had previously received two relatively ineffective lumbar interlaminar epidural steroid injections was treated with a transforaminal epidural steroid injection (right-sided L5-S1), confirmed via fluoroscopy. To confirm there was no intravascular contrast spread from the procedure, the operating clinicians performed DSA twice. They also injected a test dose of anesthetic, noting no change in the patient’s neurological status. Immediately after the patient was injected with a triamcinolone acetonide and lidocaine mixture, he reported extreme bilateral lower extremity pain, followed by “marked weakness” in the bilateral lower extremities and numbness up to the lower abdomen. Follow-up MRI, observation, and treatment revealed the patient had paraplegia resulting from acute spinal cord infarction, producing persistent bilateral lower extremity paralysis. The authors noted that this case illustrates that “even in well-trained hands,” DSA may not be sufficient to identify potentially severe adverse events associated with lumbar transforaminal epidural steroid injection.

Minimally Invasive Approach to Treating Thoracic Disc Herniation

Several current surgical approaches to treating thoracic disc disease are unsatisfactory to many patients because they require extensive surgery and prolonged hospitalization, and are associated with a range of potentially serious complications and post-surgery alterations in quality of life. Offering a potential alternative for select patients, Datta and Kaul presented the case of a 31-year-old woman with several thoracic disc herniations who had previously opted for conservative treatment (physical therapy, epidural steroid injections, thoracic medial branch blocks, etc) rather than undergo extensive surgery. When her condition proved refractory to these measures, the authors elected to perform a percutaneous endoscopic thoracic discectomy (PETC), which necessitated extensive pre-operative planning requiring a thoracic discography, MRI, and CT. In their write-up of the case, the authors discussed the anatomical features of the thoracic spine that complicate the treatment of thoracic disc herniations, outlined several potential complications associated with conventional posterior, posterolateral, and anterior approaches to treatment, explained the thinking that led them to select PETC for this patient, which produced an excellent outcome, “without the need for hospitalization or bleeding complications and without retraction of the spinal cord in the presence of significant adhesions to the dural sac.”

With more patients with chronic non-cancer pain than ever being prescribed opioids as part of their treatment regimen, the potential that these patients may abuse or misuse their opioid medications is a key concern for clinicians.

Test That Identifies Potential Genetic Causes of Variations in Drug Metabolism is a Key Part of Risk Monitoring in Opioid Therapy

With more patients with chronic non-cancer pain than ever being prescribed opioids as part of their treatment regimen, the potential that these patients may abuse or misuse their opioid medications is a key concern for clinicians. Urine drug testing (UDT) is the current standard for monitoring patients for adherence to opioid treatment, as it is “easy to use, inexpensive, and allows for the presence or absence of certain drugs to be evaluated with good specificity and sensitivity.” However, clinicians who incorporate UDT into their practice should be aware that test results can be influenced by variability in pharmacokinetics, pharmacodynamics, and pharmacogenetics, potentially producing test results that show unexpected levels of prodrugs and metabolites.

Studies have shown that a substantial portion of the population has genetic abnormalities that affect the Cytochrome P450 2D6 (CYP2D6) enzyme, which is responsible for the metabolism of many prescription pain medications. These genetic variations can produce a high degree of variability in the rate at which individuals metabolize certain medications (they are often classified as extensive, intermediate, poor, and ultra-rapid metabolizers). The rapidity with which a patient’s metabolism converts an inactive prodrug to its active (metabolite) form can produce irregular or unexpected UDT results and make it appear as if the patient has not been adhering to his or her prescribed treatment regimen.

To illustrate this phenomenon and provide an opportunity to discuss potential clinical implications, Schiller, Eisenstat, Kim, et al, from the Department of Anesthesiology, Center for Pain Management, at Stony Brook University Medical Center, NY, presented the case of a woman who was being treated with hydrocodone/acetaminophen 10/325 for her chronic low back pain, which the patient claimed produced minimal pain relief. Her UDT results showed the presence of hydrocodone, as expected, but below-anticipated levels of hydromorphone (the active metabolite of hydrocodone). Repeat testing again produced results consistent with aberrant behavior, though the patient insisted she was correctly following her prescription regimen. CYP2D6 genotype testing revealed that she had an abnormality that resulted in her being an intermediate metabolizer, which would explain her UDT results.

The authors noted that the results of genetic testing in this case not only explained the suspicious test results, the fact that the patient was not efficiently metabolizing hydrocodone into its active metabolite hydromorphone also explained why she received inadequate analgesia from her treatment. Armed with this knowledge regarding the patient’s metabolism, rather than increasing her dose of hydrocodone, her prescriber switched her to treatment with hydromorphone, resulting in substantially improved pain relief.

The authors cautioned that genetic testing of this kind has its limitations, and that there are other enzymes and factors that can affect how a patient metabolizes pain medications. However, with proper training and knowledge, CYP2D6 can be a valuable tool for pain management physicians.