The endogenous analgesic system may be connected to the development of chronic postoperative pain. The terms “diffuse noxious inhibitory controls” (DNIC; in animals) or “conditioned pain modulation” (CPM; in human beings), refer to a “pain inhibits pain” phenomenon whereby the activities of convergent neurons [wide dynamic range neurons (WDR neurons)] in the spinal dorsal horn and trigeminal nucleus are selectively and powerfully inhibited by the application of a stimuli to another body area distant from their excitatory receptive fields. DNIC and CPM involve a supraspinal loop, including the serotonergic and noradrenergic systems. The relationship between postoperative pain and CPM effect has been reported. Individual response to CPM can vary widely among patients. Therefore, the risk for chronic postoperative pain may be predicted by using CPM tests before surgery. In this review, we discuss the neuronal mechanisms of DNIC and CPM, the methodology of CPM, and the potentiality of CPM as a screening test for chronic postoperative pain.

This retrospective study investigated 133 patients who received sinuvertebral nerve blocks (S-V blocks) over 157 sessions between 2012 and 2017. Therapeutic effects were assessed using the numerical rating scale (NRS). Treatment was considered effective in patients in whom the NRS score was reduced to ≦50％ a month after the S-V block. S-V blocks were performed under fluoroscopic guidance with patients placed in the oblique position. A nerve block needle was inserted into the dorsal fiber ring of the intervertebral disc, and a solution containing 0.5 ml of 1％ mepivacaine＋0.825 mg of aqueous dexamethasone was injected. Treatment was effective in 68 patients (51.1％). Diagnosis was established in 21 of 26 patients (80.8％). No adverse effects were observed in association with the procedure. One-year outcomes were remission with treatment completion in 23 patients. S-V blocks are useful to diagnose and treat conditions associated with the intervertebral discs.

Serotonin syndrome is caused by excessive serotonin stimulation at the central and peripheral nerve postsynaptic synapse. Patients present with changes in mental status and symptoms of neuromuscular and autonomic dysfunction. We report 3 cases of serotonergic disorder in patients with chronic pain who received a small dose of duloxetine and tramadol. Patients presented with mental symptoms, sweating, palpitations, and tremor after receiving duloxetine and tramadol. Notably, immediate symptomatic improvement was observed with discontinuation of both medicines or of duloxetine alone. Patients were diagnosed with serotonin syndrome based on careful history-taking. Tramadol metabolism is inhibited by duloxetine (which inhibits CYP2D6). Therefore, it is speculated that the increase in blood concentration of tramadol caused serotonin excess in these patients. Inhibition of tramadol metabolism was attributed to the administration of bicalutamide (CYP3A4 inhibitor) in 1 patient. Clinicians must be aware of drug-drug interactions and closely monitor adverse effects, particularly in patients with chronic pain who receive polypharmacy.

We report the role of methadone and intrathecal analgesia in successfully treating intractable cancer pain associated with a malignant tumor in a pediatric patient. Case: A 12-year-old girl presented with a history of a malignant peripheral nerve sheath tumor when she was 3 years old. At 12 years of age in June 2016, she developed paraplegic symptoms secondary to thoracic cord infiltration. Pain worsened and was refractory to oxycodone. In October of the same year, she was transferred to the palliative care ward of our hospital. Oxycodone was switched to methadone, which led to pain relief by the 7th day of hospitalization. On the 33rd of hospitalization, achalasia worsened with disease progression, and intrathecal analgesia was initiated. Pain was well controlled until her death. To date, the concomitant use of methadone and intrathecal analgesia has not been reported in Japan. We report the use of this combination for safe and effective management of intractable cancer pain in pediatric patients.

Spinal muscular atrophy (SMA) is a disease characterized by progressive loss of motor neurons causing progressive muscle atrophy. To date, no definitive treatment is available, and management primarily involves symptomatic treatment, such as artificial ventilation for respiratory failure, among other such strategies. Nusinersen, a new drug that was introduced in Japan in 2017, can improve motor function in these patients. However, nusinersen needs intrathecal administration, which serves as a disadvantage. Lumbar puncture for intrathecal administration can be challenging in patients with advanced scoliosis. We report 2 cases of X-ray fluoroscopic-guided lumbar puncture performed in patients with SMA and concomitant advanced scoliosis. Case 1: A 29-year-old woman with SMA and advanced scoliosis underwent successful lumbar puncture using X-ray fluoroscopy for intrathecal administration of the drug. Case 2: A 15-year-old female adolescent with SMA and advanced scoliosis was scheduled for intrathecal drug administration, and the drug was successfully administered under fluoroscopy guidance, as in case 1. We conclude that X-ray fluoroscopy is useful for lumbar puncture in patients with advanced scoliosis.