Thalamic ventral posterior nucleus (VPN) volume is associated with neuropathic pain intensity in patients with aquaporin-4-immunoglobulin G (AQP4-IgG) positive neuromyelitis optica spectrum disorders (NMOSD), according to study results published in Multiple Sclerosis and Related Disorders.
Chronic pain is common among patients with NMOSD, defined as chronic relapsing inflammatory disorders of the central nervous system associated with pathogenic IgG antibodies against astrocytic AQP4. Previous studies suggested an association between neuropathic pain and spinal cord lesions and between pain intensity and thalamic volume.
The objective of the current study was to explore VPN volume changes in patients with neuropathic pain, compared with pain-free patients and to determine the link between VPN volume and pain intensity in patients with AQP4-IgG seropositive NMOSD.
Study researchers conducted a cross-sectional study, using the PainDetect Questionnaire to assess neuropathic pain intensity. They utilized magnetic resonance imaging with a multi-atlas-based automated segmentation approach to determine spinal cord lesion number and location, as well as VPN volume.
Of 76 patients screened, this study included 32 (mean age, 51.1 years; 96.9% women) patients with AQP4-IgG positive NMOSD and 37 (mean age, 47.8 years; 86.5% women) age- and sex-matched healthy controls.
Of 32 study participants, 25 (78.1%) suffered from neuropathic pain and 7 patients were pain-free. There was no difference between those with pain and without pain with regards to age, sex, disease duration, number of previous myelitis episodes and depression.
Mean VPN volume was not significantly different between patients with and those without pain (667.5 mm3 vs 699.0 mm3, respectively; P =.533), or between patients with NMOSD and healthy controls (674.4 mm3 vs 679.7 mm3, respectively; P =.674).
In patients with neuropathic pain there was an inverse correlation between average VPN volume and mean pain intensity (rho = -0.486; P =.019) and highest pain intensity (rho = -0.593; P =.003). The association between VPN volume with average and highest pain intensity remained significant after adjustment for age, myelitis count, and spinal cord lesion location. No other thalamic nuclei volumes correlated with measures of pain intensity.
Thoracic involvement was more frequent in patients with neuropathic pain, compared with pain-free patients (75% vs 14.3%; odds ratio, 16.110; 95% CI, 1.52-867.1).
The study had several limitations, including the relatively small sample size, cross-sectional design, missing data on pain duration, and potential selection bias.
“[O]ur study suggests that the thalamic VPN influences the severity of neuropathic pain in patients with AQP4-IgG-positive NMOSD. Moreover, we confirm the high prevalence of neuropathic pain and its association with spinal cord lesions in NMOSD,” concluded the study researchers.
Asseyer S, Kuchling J, Gaetano L, et al. Ventral posterior nucleus volume is associated with neuropathic pain intensity in neuromyelitis optica spectrum disorders. Mult Scler Relat Disord. Published online, October 12, 2020. doi:10.1016/j.msard.2020.102579