Aim:
To describe a case of acquired Periodic Alternating Nystagmus (PAN) with oscillopsia treated with botulinum toxin injections into four horizontal rectus muscles.
Method:
A 22-year-old woman presented with sudden onset PAN. The only abnormality found following extensive investigations was bilateral superior cerebellar peduncle atrophy on MRI. Various treatment options were discussed, with reasonable response to baclofen, less so to gabapentin. However, she was keen for a longer-term solution without medication-related adverse effects. She was offered weakening of all four horizontal rectus muscles recessions, either with botulinum toxin or surgery, and she opted for the former to simulate the effects of surgery. 2.5 units of Dysport were injected into each horizontal rectus muscle without adverse effect.
Results:
Off all treatment, Snellen Visual Acuity (VA) was 6/12 in either eye with oscillopsia as a result of the PAN. Post-botulinum toxin VA was 6/5 and 6/6 on the right and left respectively, with both subjective and objective improvement in the nystagmus and oscillopsia.
Conclusion:
Botulinum toxin has an important role in the nystagmus and strabismus clinics. Depending on the circumstances, it may be used as either long term treatment, or for surgical planning to simulate the effects of surgery. In this case, the effects were equivalent to high dose of baclofen and four horizontal rectus muscles recessions, which she underwent when the effects of the botulinum toxin had worn off. Botulinum toxin could be considered as a treatment option in acquired PAN, particularly in women of childbearing age and/or if intolerant or refractory to medical treatment, but ideally not as a long-term treatment option.