The role of sensory fiber demography in trigeminal and postherpetic neuralgias

Abstract

In this study, we systematically investigated fiber demography, based on function and distribution, from the periphery to their destinations in the various central (sub) nuclei in the trigeminal brainstem nuclear sensory complex. Conventional and novel compelling information is provided, demonstrating that the ratio and somatotopy of types A and C sensory fibers at the site of a lesion can elucidate important puzzles in TNP disorders. For instance, we explain how of a major shift in the fibers' direction and ratio at the level of the trigeminal root entry zone (REZ) influences the pathophysiology of pre- and typical trigeminal neuralgia. As a result, there is a high A/C ratio of oral and peri-oral fibers in the supero-medial region of the REZ, which is mostly susceptible to vascular compression. However, this A/C ratio varies considerably at lower proportions in other areas along the peripheral trigeminal pathway, where an injury (viral, vessel compression, or trauma) can lead to a broader spectrum of fiber involvement and, consequently, pain outcome. In summary, we explain how fiber demography can influence pain quality, location, temporal features, progress, and treatment prognosis of TNP in those patients who develop it.

Figure 1.

Clinical characteristics and pathophysiology associated with typical trigeminal neuralgia (typical-TN). *All images are original, with the exception of the left table (a), which was reprinted, with small adaptations, from DaSilva and Acquadro (2005), with permission from SNELL Medical Communication Inc. **The A- and C-fiber distribution in the trigeminal brainstem nuclear sensory complex, located in the center table, is based on available animal studies.

Figure 2.

Clinical characteristics and pathophysiology associated with atypical trigeminal neuralgia (atypical-TN). *The left table (a) was reprinted, with small adaptations, from DaSilva and Acquadro (2005), with permission from SNELL Medical Communication Inc. **3-D image modified from DaSilva (2002). ***fMRI images reprinted from DaSilva et al. (2002), with permission from the Journal of Neuroscience, and from Borsook et al. (2003), also with permission from the Journal of Neuroscience.

Figure 3.

Clinical characteristics and stages of varicella zoster virus (VZV) infection related to the pathophysiology of post-herpetic neuralgia (PHN). All images are original with the exception of: *the left table (a), which was reprinted, with small adaptations, from DaSilva and Acquadro (2005), with permission from SNELL Medical Communication Inc.; and **the top images in illustration 4 (chronic pain phase), which were reprinted, with minimal adaptations, from Oaklander (2008), with permission from Elsevier, with special credit to Oaklander (2001), also reprinted with permission from Elsevier.