ATYPICAL REVERSED PAROXYSMAL POSITIONING NYSTAGMUS IN BENIGN PAROXYSMAL POSITIONAL VERTIGO

An atypical paroxysmal positioning nystagmus (PPNy), ''reversed'' in i ts directional components, is a rare finding in patients suffering fro m benign paroxysmal positioning vertigo (BPPV). It poses problems of p athophysiogenetic interpretation, differential diagnosis with a CNS le sion and therapeutic strategy. Such a finding was observed in 7 patien ts (out of a total of 450 BPPV) and took on the typical PPNy pattern a fter repeated diagnostic manoeuvres. These aspects are incompatible wi th the ''heavy cupula'' mechanism (cupulolithiasis) and are better exp lained by the presence of ''free endolymph aggregates'' (canalolithias is) within the posterior semicircular canal (p.s.c). Moreover, canalol ithiasis would also permit a more convincing interpretation of all the clinical findings observed in typical p.s.c.-BPPV.