Abstract
Ophthalmoplegic migraine (OM) is an isolated ocular motor cranial neuropathy that improves spontaneously within weeks, accompanied or preceded by a migraine-like headache. The attacks are recurrent and usually involve the oculomotor nerve, although abducens palsies and, rarely, trochlear palsies have been reported. It typically begins in childhood. OM was initially classified in the International Classification of Headache Disorders, 1st edn (ICHD-I) as a primary headache disorder and a subtype of migraine. It was reclassified as a cranial neuralgia in ICHD-II following reports of gadolinium enhancement of the oculomotor nerve during attacks of OM. The International Headache Society (IHS) Classification Committee expressed their doubt that OM ‘has anything to do with migraine’ because of its long duration and gadolinium enhancement (1); this is reflected in the comment within ICHD-II suggesting that OM is a recurrent demyelinating neuropathy (2).
Two recent publications have re-opened the debate on the appropriate classification of this entity. Lal and colleagues described 62 patients evaluated in India between 1996 and 2005, aged 15–68 years (3). All of their patients had a past history of uncontrolled migraine and most experienced a flurry of severe migraines attacks ≥ 2 weeks prior to the OM. The headache associated with the ophthalmoplegia was typically severe. In contrast to children with OM, the abducens nerve was affected more commonly (56.5%) than the oculomotor (33.9%) or trochlear (8.1%) nerves; one patient had two nerves involved simultaneously. Although none of their patients had nerve enhancement on neuroimaging studies, those who received steroids and migraine prophylaxis (n = 20) had a shorter recovery time compared with patients who received migraine prophylaxis alone (n = 18). Fourteen of their patients had two or more attacks.
In this issue of Cephalalgia, Lane and Davies report two cases of OM (4). The first patient had typical attacks of OM whereas the second patient experienced ‘ocular motor mononeuropathy multiplex’. He had attacks of steroid-responsive oculomotor and abducens pareses that did not improve with preventive therapy for migraine; one attack of abducens paresis was painless (others have reported painless attacks (5)). Did both of these patients have OM? Would the IHS Classification Committee acknowledge the entity of ‘acephalgic OM’? The fundamental question remains unanswered: ‘What is ‘OM?’.
The classification of headache disorders is determined by phenomenology in some cases and pathology in others. The debate regarding OM arises because the phenotype of the clinical syndrome may be associated with a demonstrable abnormality on magnetic resonance imagine (MRI) or with another secondary cause. A secondary cause may be discovered many years after the episodes begin. Postulated mechanisms for OM include microvascular ischaemia, demyelination and inflammation; the typical OM syndrome may be a manifestation of a schwannoma, lymphoma, leukaemia, post-viral syndrome, systemic lupus erythematosus, a vascular abnormality and giant cell arteritis. Many of the reported secondary causes improve with corticosteroids, which are frequently used to treat OM. However, only demyelination and microvascular ischaemia produce cranial mononeuropathies that consistently remit without treatment.
As the controversy rages, I propose considering OM as a syndrome that may be ‘primary’ or secondary. Cases in which there is no identifiable cause or cranial nerve enhancement on MRI, and the episodes remit spontaneously, may be considered a form of migraine. The OM syndrome accompanied by gadolinium enhancement of the affected cranial nerve on MRI that resolves interictally is likely to represent a recurrent demyelinating or inflammatory cranial mononeuropathy. In some cases, the enhancing cranial nerve is ultimately diagnosed as a tumour.
How can we classify this rare disorder to accommodate both the phenotype and the pathology? Perhaps we cannot, but I suggest the following definitions of OM within the ICHD-II classification system:
Diagnostic criteria:
At least two attacks fulfilling criteria B and C Headache accompanied or followed within 4 days of its onset by paresis of one or more of the third, fourth and/or sixth cranial nerves At least one episode of ophthalmoplegia resolves without therapeutic intervention The affected cranial nerve does not demonstrate contrast enhancement on neuroimaging studies during the attack Not attributed a parasellar, orbital fissure, posterior fossa lesion or other disorder.
Comment: This is a rare disorder and is occasionally manifested by acephalgic attacks. Permanent ocular motor nerve paresis may occur after repeated attacks.
Diagnostic criteria and comment: same as 1.2.7.
Diagnostic criteria:
At least two attacks fulfilling criteria B and C Headache accompanied or followed within 4 days of its onset by paresis of one or more of the third, fourth and/or sixth cranial nerves The affected nerve may demonstrate contrast enhancement on neuroimaging studies during the attack Not attributed a parasellar, orbital fissure, posterior fossa lesion or other disorder.
Comment: This is a rare disorder and is occasionally manifested by acephalgic attacks. Permanent ocular motor nerve paresis may occur.
Diagnostic criteria and comment: same as 13.17.
Primary OM would be classified as a subset of migraine with aura and secondary OM would replace the current ‘ophthalmoplegic migraine’ entry as a cranial neuropathy. Based on this classification and the description in their report, Lane and Davies’ first case would be classified as primary OM (assuming that the accompanying headache was the same as her typical migraine) and the second case as probable secondary OM. Meanwhile, Classification Committee members and neuro-ophthalmologists . . . sharpen your swords!