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In this issue of Practical Neurology, Popkirov, Staab and Stone illuminate a newly defined condition—persistent postural-perceptual dizziness or ‘PPPD’,1 ,2 a maladaptive functional syndrome in which patients feel unbalanced despite not falling, and feel that they are moving, despite being stationary. PPPD is common in specialist dizzy clinics, accounting for 10% of cases as a primary diagnosis of dizziness.3 PPPD can coexist with other causes of dizziness, such as vestibular migraine or benign paroxysmal positional vertigo, and it is in this form that it most commonly presents to a specialist dizzy clinic.
PPPD is a complex functional neurovestibular disorder thought to arise from the ‘mismatch’ between ‘bottom-up’ inputs (ie, vestibular and/or proprioceptive) and maladaptive signals from ‘top-down’ attentional control systems (ie, anxiety-driven hypervigilance). Current models show that the brain acts as a Bayesian estimator in which both prior estimates (‘beliefs’) and current information influence the state of sensory and motor processes. 4 Popkirov, Staab and Stone’s proposal for the pathophysiological model of PPPD invokes a disturbance in the brain’s Bayesian estimator, such that PPPD and functional neurological disorders in general are driven by excessively precise top-down a priori beliefs.4 However, at present, this only remains an intriguing hypothesis that requires additional testing and empirical evidence.
For PPPD, important internal estimates …
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