Botulinum toxin in fourth nerve palsies.

BACKGROUND: Botulinum toxin A (BTXA) has not been used routinely in the management of fourth nerve (IV N) palsy. However, it is known that the results of surgery can be unpredictable with a risk of over- or under-correction.

METHODS: The results were reviewed of 20 patients, aged 19-70 years, with unilateral and bilateral IV N palsies who received BTXA injections to the inferior oblique or inferior rectus muscles. The aetiology was congenital in 12 (60%), traumatic in six (30%), due to myasthenia in one (5%), and unclear in one (5%). Fifty per cent of patients had had previous strabismus surgery to a maximum of four procedures. The mean pre-injection vertical deviation was 11 prism dioptres. All but two patients had a single injection. Average follow-up was 19 months.

RESULTS: Ten patients (group I) received BTXA as a primary therapy. Following inferior oblique injection, six patients received little benefit and went on to surgery (83%) or continued with prisms (17%). Five patients from group I who had inferior rectus toxin were discharged symptom-free. Group 2 (10 patients) received BTXA for residual deviations postoperatively; in this group all except one patient with no fusion achieved long-term benefit following inferior rectus BTXA. In those who had inferior oblique injections, BTXA was useful in one patient (25%). Inferior rectus injection produced a greater chance of temporary reversal of the deviation.

CONCLUSIONS: BTXA is of greatest benefit in patients with residual deviations particularly when the inferior rectus is injected, but is of limited value as a primary therapy in chronic IV N palsy.