Downbeat nystagmus simplified. 65 π©βπ¦° with new walking difficulty and dizziness. AMPAR Ab positive. WB PET CT negative. Improvement with Rituximab 1gm/mth x 2 dosesπWhy DBN ?
The eyes tend to move down due to gravity. To counteract this the SVN sends facilitatory stimuli to the Sup rectus to move the eyes up. This is balanced by floccular inputs that inhibit this.
Floccular lesions impair this balance and the SVN to SR impulses overact causing the eyes to move up slowly. The corrective movement causes downbeat 'fast' movements seen as DBN
Hence DBN is a great localizing tool as it points to bilateral floccular lesions. In the absence of structural lesions, look for intra-axial pathologies like autoimmune/ paraneoplastic encephalitis.
Simply put , our eyes start floating up because antigravity signals are stronger than gravity signals. Correction of this leads to DBN
KISS- flocculus makes the eyes fly up. If itβs damaged you fall down fast (DBN)
Slow up and fast down- flocculus fails to fly
@vishrawji But I suppose these pathway dysfunctions can cause DBN even in the absence of gravity
If your flocculus is blown, youβre going down
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