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Anthony S. Larson, Lorenzo Rinaldo, Waleed Brinjikji, and James P. Klaas

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Sanford J. Larson, Anthony Sances Jr., Donald H. Riegel, Glenn A. Meyer, Donald E. Dallmann, and Thomas Swiontek

✓ In 18 patients with cancer and intractable pain, capacitatively coupled pulses of 0.25 msec duration were delivered transcutaneously at 100 Hz to sets of five in-line electrodes implanted subdurally over the dorsal columns. Averaged somatosensory-evoked potentials were recorded from scalp electrodes before, during, and after application of current. All but one patient experienced relief of pain during stimulation, persisting for as long as several hours afterward. Eleven patients developed hyperactive deep reflexes, pathological reflexes, and decreased perception of joint rotation, pain, and touch below the level of current application. Somatosensory-evoked potential amplitudes were markedly reduced. All neurological findings returned to control values within 1 hour after each of repeated applications of current. Histological examination of spinal cord sections from four cancer patients showed no changes secondary to long-term current application.

Similar currents were applied to the spinal cord of 15 monkeys with chronically implanted bipolar recording or stimulating electrodes over the lower, middle, and upper thoracic cord, in nucleus ventralis posterior lateralis (VPL), and over the sensory motor cortex (SMC). With application of current, the responses in VPL and SMC to peripheral stimulation were abolished. Evoked potential responses were abolished between bipolar stimulating electrodes and bipolar recording electrodes separated by the five in-line electrodes used to supply the 100 Hz current. However, when both stimulating and recording electrodes were either above or below the five in-line electrode set, evoked responses were unaffected. The findings indicate that applied currents blocked neuronal transmission by producing local changes in the cord. The prolonged alteration of cerebral evoked potentials and relief of pain, however, could also be related to involvement of supraspinal neurons.

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Joseph F. Cusick, Joel Myklebust, Mark Zyvoloski, Anthony Sances Jr., Chris Houterman, and Sanford J. Larson

✓ Experiments were performed to assess the effects of vertebral column distraction on evoked potential responses from multiple recording sites along the conducting pathway in the monkey, and on concurrent blood flows, measured with the radioactive microsphere technique, along the axis of the central nervous system. Linear distractive loads were applied until the amplitude of the evoked response was significantly reduced. In four monkeys, the loads (100 to 150 lb) were sustained, whereas in two monkeys the forces (80 to 110 lb) were relaxed. The earliest response changes were most marked in recordings dependent upon the integrity of the upper cervical dorsal columns or brain stem-lemniscal pathway. The responses returned to control levels with load relaxation, but maintenance of the tractive load produced generalized and progressive response attenuation. At selected periods of significant changes in the evoked potential response, blood flow remained stable except for the late onset of regional ischemia in the middle cervical through upper thoracic spinal cord levels in the animals undergoing sustained loads. These findings indicate that brain-stem or spinal cord dysfunction occurring with both acute and gradual elongation of the spinal canal are the result of excess tensile stress acting on fiber tracts, and the delayed onset of spinal cord ischemia is the probable result of a similar mechanical process acting upon intrinsic spinal cord blood vessels.

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Teriparatide treatment increases Hounsfield units in the lumbar spine out of proportion to DEXA changes

Presented at the 2019 AANS/CNS Joint Section on Disorders of the Spine and Peripheral Nerves

Anthony L. Mikula, Ross C. Puffer, Jeffery D. St. Jeor, James T. Bernatz, Jeremy L. Fogelson, A. Noelle Larson, Ahmad Nassr, Arjun S. Sebastian, Brett A. Freedman, Bradford L. Currier, Mohamad Bydon, Michael J. Yaszemski, Paul A. Anderson, and Benjamin D. Elder

OBJECTIVE

The authors sought to assess whether Hounsfield units (HU) increase following teriparatide treatment and to compare HU increases with changes in bone mineral density (BMD) as measured by dual-energy x-ray absorptiometry (DEXA).

METHODS

A retrospective chart review was performed from 1997 to 2018 across all campuses at our institution. The authors identified patients who had been treated with at least 6 months of teriparatide and compared HU and BMD as measured on DEXA scans before and after treatment.

RESULTS

Fifty-two patients were identified for analysis (46 women and 6 men, average age 67 years) who underwent an average of 20.9 ± 6.5 months of teriparatide therapy. The mean ± standard deviation HU increase throughout the lumbar spine (L1–4) was from 109.8 ± 53 to 133.9 ± 61 HU (+22%, 95% CI 1.2–46, p value = 0.039). Based on DEXA results, lumbar spine BMD increased from 0.85 to 0.93 g/cm2 (+9%, p value = 0.044). Lumbar spine T-scores improved from −2.4 ± 1.5 to −1.7 ± 1.5 (p value = 0.03). Average femoral neck T-scores improved from −2.5 ± 1.1 to −2.3 ± 1.0 (p value = 0.31).

CONCLUSIONS

Teriparatide treatment increased both HU and BMD on DEXA in the lumbar spine, without a change in femoral BMD. The 22% improvement in HU surpassed the 9% improvement determined with DEXA. These results support some surgeons’ subjective sense that intraoperative bone quality following teriparatide treatment is better than indicated by DEXA results. To the authors’ knowledge, this is the first study demonstrating an increase in HU with teriparatide treatment.