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Neurological Rehabilitation

Agreement Between H/M Ratio and Radionuclide Isotopic Cisternography in Assessing Intrathecal Baclofen System Function

Thursday, October 23, 2025
12:45 PM - 2:15 PM MT
Location: Kiosk 10
Disclosure(s):
Daniel Tyler Trussell, MS: No financial relationships to disclose
Stuart A. Yablon, MD: No financial relationships to disclose
Dobrivoje S. Stokic, MD: No financial relationships to disclose
Background and/or Objectives: Intrathecal baclofen (ITB) therapy uses an implanted pump and catheter system to deliver medication to the CSF. When a malfunction is suspected, the troubleshooting algorithm includes clinical assessment, pump interrogation, plain radiographs, CT, and Indium nuclear medicine imaging (NMI). Although commonly used, NMI is expensive, time-consuming, and not always available. We have shown that the H-reflex to M-wave (H/M) ratio recorded in the soleus muscle may offer a simple, sensitive, and cost-effective alternative for evaluating ITB system function. However, the two methods have not been directly compared. Therefore, this study aimed to determine the agreement between the H/M ratio and NMI in assessing ITB system function.

Design: Retrospective consecutive cohort.

Setting : Outpatient spasticity clinic at a tertiary rehabilitation center.

Participants : 24 recipients of the ITB system (17 males; mean age 40 yrs.) for spasticity of spinal (n=10) or supraspinal origin (n=14) who underwent 27 NMI and H/M ratio studies 23 days apart, on average.

Interventions: N/A

Main Outcome Measures: Absolute agreement, sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV).

Results: Of 27 studies, the H/M ratio and NMI both indicated 18 system malfunctions and 9 intact systems. They agreed in 16/18 malfunction cases and 7/9 intact cases, yielding an overall agreement of 23/27 (85%; 16 true positives, 7 true negatives, 2 false positives, and 2 false negatives). Using NMI as the reference, the H/M ratio showed 78% sensitivity (95% CI: 40%, 97%) and 89% specificity (95% CI: 65%, 99%). With an equal number of false positives and false negatives, PPV and NPV were identical to sensitivity and specificity, respectively.

Conclusions: The high agreement between the H/M ratio and Indium NMI implies that the H/M ratio may be a practical alternative or adjunct for assessing ITB system function.