Persistent postural-perceptual dizziness (PPPD): the most common cause of chronic dizziness.

Persistent postural- perceptual dizziness (PPPD) is a functional disorder that is the most frequent cause of chronic dizziness. Diagnostic criteria for PPPD were published by Bárány Society in 2017 and were then included in the International Classification of Diseases, 11th revision (ICD-11). Core symptoms are dizziness, unsteadiness or non-spinning vertigo, lasting more than three months. Persistent symptoms occur without specific provocation, but are exacerbated by upright posture/walking, active or passive motion, and exposure to moving or complex visual stimuli. An acute or episodic vestibular disorder often precedes the onset of PPPD, but conventional vestibular function tests typically show normal results. Studies using resting-state functional MRI have revealed that functional connectivity between the vestibular cortex and visual areas were low, while that between the somatosensory and visual areas was high, suggesting sensory upweighting of visual and somatosensory information. Such central changes have been shown to associate with peripheral hyper-responsiveness as demonstrated by visual stimulus-loaded posturography and head-roll tilt subjective visual vertical testing, which detects visual and neck proprioceptive hypersensitivity, respectively. As a result, symptoms are exacerbated by visual stimulation or somatosensory input associated with body motion. After visual stimulation, gaze stability remains reduced, which would account for the prolonged dizziness induced by visual stimuli. Pharmacological treatments using serotonergic anti-depressants, vestibular rehabilitation, and cognitive behavioral therapy have been shown favorable effects; however, they are not always effective for all patients. There is an urgent need to establish novel treatments tailored to the pathophysiology of PPPD, i.e., sensory upweighting of visual/somatosensory inputs.