Longitudinal Microglial Imaging Study

1 Background and Rationale

Progressive post-exertional malaise (PEM) worsening suggests cumulative biological damage, particularly in the central nervous system. Microglial activation, a hallmark of neuroinflammation, may represent a measurable correlate of PEM progression. TSPO (translocator protein) positron emission tomography (PET) imaging provides a non-invasive method to quantify microglial activation in vivo. This study would establish TSPO-PET as a biomarker for neuroinflammation severity and its relationship to PEM trajectories.

2 Study Design

2.1 Design Overview

Prospective longitudinal observational study with serial TSPO-PET imaging and detailed PEM documentation.

2.2 Participants

  • n=50 ME/CFS patients (ages 18–60)
  • Documented PEM with variable severity trajectories (stable, slowly progressive, rapidly progressive)
  • Mild to moderate severity (able to tolerate imaging procedures)
  • Disease duration \(\geq\) 6 months
  • No contraindications to PET imaging

2.3 Stratification

Stratified by PEM trajectory at baseline:

  • Stable PEM (n=15): Crash frequency and severity unchanged over past 6 months
  • Progressive PEM (n=20): Increasing crash frequency or severity over past 6 months
  • Rapidly Progressive PEM (n=15): Significant functional decline over past 3 months

3 Assessment Schedule

  • Baseline: TSPO-PET imaging, detailed clinical assessment, 6-month pre-baseline PEM diary retrospective review
  • 6 months: TSPO-PET imaging, PEM diary review, functional assessment
  • 12 months: TSPO-PET imaging, comprehensive clinical and biomarker assessment
  • Continuous: Electronic PEM crash diary with severity ratings (1–10 scale), recovery duration documentation

4 Measures

4.1 TSPO-PET Imaging

  • 11C-PBR28 or 18F-DPA-714 radioligand (TSPO-specific tracers)
  • Standardized uptake value (SUV) analysis in predefined regions of interest (basal ganglia, thalamus, brainstem, prefrontal cortex)
  • Distribution volume ratio (DVR) to derive binding potential
  • Whole-brain voxel-wise analyses to identify activation hotspots

4.2 PEM Documentation

  • Crash trigger (physical, cognitive, emotional, mixed)
  • Pre-crash activity level (hours of exertion)
  • Crash severity (1–10 scale, anchored descriptions)
  • Recovery duration (days to baseline)
  • Associated symptoms (cognitive dysfunction, pain, autonomic symptoms)

4.3 Clinical and Functional Measures

  • Bell Disability Scale
  • DSQ-PEM
  • Cognitive assessment (Montreal Cognitive Assessment)
  • Autonomic testing (NASA Lean Test, HRV)
  • Inflammatory markers (high-sensitivity CRP, cytokine panel)

5 Outcomes

5.1 Primary Outcomes

  • Correlation between TSPO-PET signal intensity at baseline and PEM recovery time at 12 months
  • Differences in baseline TSPO-PET signal between progressive and stable PEM groups
  • Change in TSPO-PET signal from baseline to 12 months as a function of PEM trajectory

5.2 Secondary Outcomes

  • Correlation between TSPO-PET signal and functional decline (Bell scale change)
  • Regional specificity: Which brain regions show signal changes most relevant to PEM?
  • Effect of LDN treatment (in patients who elect to initiate) on TSPO-PET signal reduction
  • Correlation of TSPO-PET with systemic inflammatory markers

6 Analysis Plan

  • Spearman or Pearson correlations between TSPO-PET SUV and PEM recovery time
  • ANOVA comparing TSPO-PET signal across PEM trajectory groups
  • Mixed-effects models with random intercepts for subjects to assess PET signal trajectory
  • ROI-specific and voxel-wise analyses with multiple comparison correction
  • Adjustment for age, sex, disease duration, and baseline severity

7 Sample Size and Power

With n=50 participants and 3 imaging timepoints per subject:

  • 80% power to detect Spearman \(\rho\)=0.35 between TSPO-PET and PEM recovery time at \(\alpha\)=0.05
  • Sufficient for subgroup analyses by PEM trajectory
  • Adequate for exploratory regional analyses

8 Expected Outcomes and Implications

If correlations are significant:

  • Establishes TSPO-PET as biomarker for neuroinflammation severity in ME/CFS

  • Validates use of TSPO-PET as clinical trial outcome measure

  • Informs mechanism of LDN efficacy (microglial suppression)

  • Identifies patients at high risk for PEM progression If results are null:

  • Suggests microglial activation is not primary driver of PEM progression

  • Redirects focus toward other neuroinflammatory mechanisms

  • May indicate TSPO is insufficient marker (astrocytic activation, other glia)