Posterior semicircular canal paroxysmal positional vertigo triggers a new type of windmill nystagmus

Periodic alternating nystagmus is a rare condition characterised by spontaneous horizontal nystagmus that periodically reverses direction, indicating an alteration of the velocity storage mechanism. Windmill nystagmus is a peculiar and rare variant of periodic alternating horizontal nystagmus with a superimposed periodic alternating vertical nystagmus. It is generally observed in blind patients.

This paper presents the unique case of a normally sighted patient with a windmill nystagmus triggered by an episode of benign paroxysmal positional vertigo due to bilateral posterior canalolithiasis. Videonystagmography revealed an anticlockwise up-beating nystagmus followed by a clockwise down-beating nystagmus with a cycle lasting 2 minutes, followed by a brief burst of horizontal left-beating nystagmus.

This case report represents the first observation of a new type of windmill nystagmus, probably provoked by a malfunction of the velocity storage mechanism, gaze-stabilisation and short-adaptation networks, with a loss of cerebellar inhibition.