LETTER TO THE EDITOR A rare case of paroxysmal diplopia: ocular neuromyotonia Maria Elena Pessa 1 & Lorenzo Verriello 2 & Giada Pauletto 2 & Gian Luigi Gigli 1 & Mariarosaria Valente 1 Received: 7 March 2018 /Accepted: 26 May 2018 # Springer-Verlag Italia S.r.l., part of Springer Nature 2018 Dear Editor, Ocular neuromyotonia (ONM) is a rare disorder characterized by episodic spasms of extra-ocular muscles, resulting in par- oxysmal diplopia. These spasms occur spontaneously or after sustained gaze in certain directions. Patients may show signs of ophthalmoparesis between attacks. We describe a case of ONM, following nasal irradiation. A 70-year-old woman came to our attention for a 1-year history of intermittent horizontal diplopia, associated with transient esotropia and pulling sensation in the left eye (Fig. 1). Episodes typically lasted 1–2 min and resolved spontane- ously. Precipitating factors were not reported. Medical history disclosed a previous right breast cancer, treated with mastectomy and chemotherapy, 11 years before. Moreover, 10 years before, the patient underwent surgery for inverted papilloma of left mean nasal meatus, with post- operative local irradiation consisting of 50 Gy in 25 treatments. Neuro-ophthalmologic examination showed normal visual acuity, visual field, and fundi. During quiescent period, the patient presented mild esotropia and ptosis of the left eye, with slight impairment of upward and downward rotation of the left eye. The left eyelid, mild ptotic in primary position, was elevat- ed in down gaze (oculomotor synkinesis). The right pupil was 6 mm diameter and normally reactive to light; the left pupil was 4 mm diameter with reduced reac- tion to light. Ptosis and limitation of eye movement suggested a mild right third nerve paresis, likely due to irradiation. Sustained adduction of the left eye for 15 s resulted in paroxysmal spasm of the left medial rectus, with restriction of all ocular movements of the left eye. The spasms lasted about 1 min and 45 s and they resolve spontaneously. During attacks, no changes in upper lid position and pupil size were observed. Spasms could be easily reproduced and the typical pattern suggests medial rectus involvement. Neurological examination was otherwise normal. The results of routine blood tests and thyroid function tests were normal. Repetitive nerve stimulation (RNS) and acetylcholine re- ceptor antibody study were negative. Computed tomography (CT) of facial bones with and with- out contrast enhancement ruled out tumor recurrence. Magnetic resonance imaging (MRI) with contrast and MRI cerebral vessel angiography studies did not show any intracra- nial abnormality, especially in the midbrain. Treatment with carbamazepine 200 mg twice a day resulted in a dramatic improvement of symptoms within a week. Partial third nerve paresis remained unchanged. After 3 months of treatment, the patient reported occasional symptoms of very short duration; no further attacks could be elicited. ONM has been described in thyroid eye disease, intracra- nial tumors, following irradiation of the skull base and as consequence of neurovascular conflict [1]. Many cases remain idiopathic [2]. Ephaptic neural transmission through lateral contact be- tween nerve fibers (rather than across synapses) is a potential mechanism of ONM. Other possible mechanisms include dys- function of ionic channels in the neuronal cell membrane or axonal hyperexcitability due to denervation [3]. The latter hypothesis is supported by the therapeutic response to mem- brane stabilizer as carbamazepine. Differential diagnosis of ONM encompasses ocular myas- thenia, cyclical oculomotor spasm, and superior oblique myokymia (SOM). * Maria Elena Pessa marialen@gmail.com 1 Neurology Clinic, Azienda Ospedaliero Universitaria Santa Maria della Misericordia, Udine, Italy 2 Neurology Unit, Azienda Ospedaliero Universitaria Santa Maria della Misericordia, Udine, Italy Neurological Sciences https://doi.org/10.1007/s10072-018-3460-9