Brachial Neuritis

My wife is quite some way down the road in recovering from Brachial Neuritis, which has also caused an associated Phrenic Nerve palsy.

She suffers badly from a persistent irritant-type cough, which has no apparent physical cause. This is being controlled with Codeine, which unfortunately has the side effect of causing skin lesions by the release of histamine.

We are theorising that the cough is being caused by an involvement of the Vagus nerve in the Brachial Neuritis, and our family physician also takes that view. (Unfortunately the neurologist doesn't!!).

Do you have any thoughts on whether it's possible that the Vagus nerve has been implicated, and if so, what are the chances of spontaneous recovery?