Adult-onset recurrent painful ophthalmoplegic neuropathy displaying atypical oculomotor nerve gadolinium-enhancement pattern in the orbit and cavernous sinus

Dear Editor,

We read with great interest the review article in Cephalalgia entitled ‘Ophthalmoplegic migraine: From questions to answers’ by Ambrosetto et al. (1). The authors pointed out that, in adult-onset recurrent painful ophthalmoplegic neuropathy (RPON, code 13.9 of ICHD-3 beta), the magnetic resonance imaging (MRI) finding shows no gadolinium enhancement or nerve thickening. We experienced an adult-onset case of RPON in which fat-suppressed post-contrast T1-weighted imaging (T1WI) and T2-weighted imaging (T2WI) were useful in detecting lesions within the orbit and cavernous sinus.

A 42-year-old woman presented with recurrent throbbing headaches in the right occiput followed by right ptosis and ophthalmoparesis of inward and vertical movements. She experienced these symptoms approximately 30 times in the 22 years since the first attack. The symptoms resolved within two months. After excluding cerebral aneurysm, Tolosa–Hunt syndrome, sarcoidosis, diabetes, thyroid dysfunction, collagen diseases and meningitis, we diagnosed RPON.

Ten cranial MRI examinations were conducted over six years using a 1.5-T unit. High spatial resolution thin-slice fat-suppressed T2WI was added to conventional whole brain MRI in six examinations. Only one conventional whole-brain MRI detected slight abnormal enhancement of the right oculomotor nerve at the root exit zone that was performed one week after the onset of oculomotor symptoms (Figure 1(a)). In contrast, obvious enhancement of the right oculomotor nerve within the orbit and cavernous sinus was identified in all high-resolution fat-suppressed post-contrast T1WIs of the orbit performed during an ictal period (Figure 1(b)). The magnitude of enhancement was greater 1 week after the onset of the oculomotor symptoms compared with that after three and eight weeks. The enhancement disappeared during the interictal period. Further, fat-suppressed T2WIs of the orbit and cavernous sinus showed swelling and abnormal hyperintensities of the oculomotor nerve during a paroxysmal period (Figure 1(c)). These alterations emerged in parallel with the disease activity. It is noteworthy that conventional whole-brain T2WIs did not detect such abnormalities. OPEN IN VIEWER

RPON, formerly known as ophthalmoplegic migraine, is a rare disorder and its onset occurs usually in childhood. Enhancement has been observed almost exclusively in paediatric patients (1,2) and only rarely in adults (1,3). In a series of 45 adult patients with RPON reported by Lal et al., the authors claimed that none of the patients exhibited abnormal enhancement of the ocular motor nerves (3). The site of abnormal enhancement of ocular motor nerves associated with this disease is typically at their root exit zones (2). In our case, high-resolution thin-slice MRI with the fat suppression technique clearly detected abnormal enhancement of the oculomotor nerve within the orbit and cavernous sinus. Further, fat-suppressed T2WI of the orbit identified the changes in the calibre and internal signal intensity of the oculomotor nerve.

Our experience raises the possibility that an inflammatory process at the peripheral site of the ocular motor nerves may play an important role in the pathophysiology of RPON and that high-resolution thin-slice fat-suppressed MRI of the orbit should be included in MRI studies to detect this overlooked aspect of the disease.