Commentary: Is There an "Acquired Idiopathic Head-Shaking Nystagmus?": A Discussion of Mechanisms and Clinical Implications Based on a Case Report.

Abstract

A commentary on 'Is There an "Acquired Idiopathic Head-Shaking Nystagmus"?-AWe read the paper by Filippopulos FM and his colleagues with great interest. 1 This report described a patient with recurrent episodes of vertigo prompted by fast head movement. As the authors noted, we previously reported a group of patients with recurrent spontaneous vertigo with interictal HSN (BRV-HSN) in the absence of peripheral vestibulopathy as was documented by caloric, head-impulse, or rotatory chair tests. Even though we could not assess HSN in those patients with BRV-HSN during the attacks, the only difference between the BRV-HSN and aiHSN appears to be the absent HSN between the attacks in aiHSN. Given the 1) increased time constants of the HSN and rotatory nystagmus, 2) emergence of the HSN even with a short duration of head-shaking, and 3) good responses to baclofen, we proposed that unstable and asymmetric VSM may be the cause for vertigo and BRV-HSN. 2 Apparently, the characteristics of HSN observed in the patient reported by Filippopulos FM, et al. 1 do not seem to differ from those observed in our patients with BRV-HSN. Thus, the BRV-HSN and aiHSN may lie on the same spectral line due to a common pathomechanism (unstable and asymmetric VSM), rather than distinct disease entities. In addition, the clinical presentation does not escape from the umbrella term of BRV.