Authors' reply.

Dear Sir,

We would like to thank Dr. Venugopal for his inputs pertaining to our paper, “Sankara Nethralaya Abducens Nerve Palsy: Report one.”[1] The author has pointed out that three of our patients had upper respiratory tract infections (URTIs) and three more had prior viral illnesses. Furthermore, the author has also mentioned that middle ear infection may cause isolated the sixth nerve palsy without petrositis and raised intracranial tension. Finally, Dr. Venugopal has summarized that if the sixth nerve palsy develops in a patient undergoing treatment for URTI and/or chronic suppurative otitis media (CSOM), neuroimaging should be considered.

We agree with the author's recommendation that that, if the sixth nerve palsy develops in a patient undergoing treatment for URTI and/or CSOM, neuroimaging should be considered. However, none of the patients in our cohort had any concurrent infection. As we have mentioned in the manuscript, six cases were attributed to “preceding” history of infection (three URTI and three viral illnesses). To further clarify the issue, all these patients had a prior history of URTI and viral infections, for which they had received treatment and were no longer on medication. More importantly, neuroimaging was not deferred in any of these patients. It was only after all of these six patients had undergone imaging and neuroimaging yielded no positive findings in these patients that the preceding viral illnesses were considered as the likely etiology for the nerve palsy. The exact cause in these cases may have an immunological basis as is seen in other cases of parainfectious neuropathy or viral neuritis.[23]

With regard to the sixth nerve palsy presenting in cases of CSOM, it must be borne in mind that acute hearing loss is the most common symptom seen in CSOM.[4] Hearing loss in the presence of the sixth nerve palsy would not be classified as “isolated” nerve palsy and would warrant immediate neuroimaging. Our study and the proposed algorithm focused solely on isolated, nontraumatic, acquired sixth nerve palsy.

We agree with the authors that Varicella vasculopathy may be considered as a differential diagnosis for isolated cranial nerve palsy, but it should be borne in mind that it is extremely rare. We appreciate the author's efforts in enriching literature on this topic.

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Nil.

Conflicts of interest

There are no conflicts of interest.