We have read with interest the letter of Kanazawa 1 about improvement of apraxia of eyelid opening (AEO) with botulinum toxin A.
The term AEO defined as an intermittent inability to open the eyes voluntarily is not a specific entity; it is only a clinical sign whose physiopathological origin is variable. It may be caused by an involuntary inhibition of levator palpebrae superioris (IILPS) or a blepharospasm restricted to the pretarsal portion of the orbicularis oculi (OO) called pretarsal blepharospasm (BSP). [2][3][4] As their clinical appearance are similar, because in both disorders there are not visible contraction of the orbicularis oculi, only a simultaneous electromyographic recording activity from the LPS and pretarsal and orbicular portion of OO can determine its origin. 4,5 In Kanazawa et al.'s cases, the diagnosis was only made by clinical aspect using the ambiguous and unspecific term of AEO.
Their patients improved with botulinum toxin A, so the authors suggested that "AEO associated with these neurodegenerative diseases constitutes a form of eyelid dystonia rather than apraxia, even when no overt blepharospasm is observed." Actually, AEO and BSP are not excluding terms; as we stated previously, AEO is only a clinical sign and furthermore can be the result of a pretarsal BSP that can be present even in the absence of a manifest blepharospasm.
The best method to disclose the underlying mechanism of impairment of eye lid opening in these three patients would have been an eye-lid electromyography recording. Probably, this EMG record would have showed a pretarsal BSP, whereas an IILPS would have not; this would explain why all of them improved with botulinum toxin A.
Therefore, the AEO improvement with botulinum toxin is not related with the association to neurodegenerative diseases, as Kanazawa et al. suggests, but rather with its physiopathological substrate. Finally, we think it would be more appropriate to conclude that botulinum toxin could be a good treatment only for the cases in whom the AEO is caused by BSP but not when the origin is an IILP, as other authors described previously. 4,6