“light Cupula” – New Perspective of Otolith Independent Benign Paroxysmal Positional Vertigo

Benign paroxysmal positional vertigo (BPPV) is one of the most common causes of recurrent vertigo and is characterized by transient vertigo and nystagmus elicited by change of head position. Direction-changing positional nystagmus (DCPN) is typically observed upon head turning to either side in supine position in patients with horizontal canal (HC) BPPV. The geotropic nystagmus of HC canalolithiasis is transient, has short latency, and is either weakened or lost after repetitive examination (fatigability). However, clinicians sometimes see patients with relatively long-duration geotropic DCPN without latency and fatigability. Recently, the concept of a “light cupula”, exhibiting persistent geotropic DCPN, has been introduced. The theory of light cupula indicates cupula with lower specific gravity than the surrounding endolymph. The characteristics of nystagmus in these patients are as follows: 1) a null plane at which nystagmus ceases can be found when the patient’s head is turned to the affected ear for some degrees, 2) horizontal nystagmus towards the affected side in bowing (nose-down) position, 3) horizontal nystagmus towards the healthy side in leaning or supine position, and 4) persistent geotropic DCPN without latency when the patient’s head is turned to the right or left in supine position. In this session, we would like to discuss about this phenomenon and its clinical implications.