Sir,

Whereas exercise-induced visual loss is usually due to demyelinating optic neuropathy, the much less common entity of exercise-induced double vision is usually due to intracranial glioma. We report an unusual case of exercise-induced double vision highlighting the importance of neuroimaging in such cases.

Case report

A 14-year-old male presented with an 18 months history of double vision only while running. His right eye was noted to turn inwards. The double vision resolved after 3–4 min rest. It did not occur with hot baths or when he was tired. He denied any other neurological symptoms.

There was a small right esotropia (18 Δ for distance), with bifoveal fixation and 60 s of arc stereoacuity (TNO test) but a positive four-prism dioptre test with the right eye. Extraocular movements and saccades were normal on clinical examination but Hess chart showed mild limitation of abduction of the left eye. After exercise there was double vision with a moderate right esotropia (40 Δ). Extraocular movements and saccades were still normal.

The double vision resolved and the ocular alignment returned to the preexercise state after 5 min rest. Neurological examination was normal.

Magnetic resonance imaging (MRI) showed an extensive T2 high-signal lesion involving both sides of the pons extending into the medulla with mild swelling but no contrast enhancement, consistent with a brainstem glioma (Figure 1).

Figure 1
figure 1

MRI demonstrating brain stem glioma.

Full size image

Cerebrospinal fluid examination including cytology was normal. Initially following radiotherapy (54 Gy in 30 doses over 6 weeks) there was clinical deterioration with diplopia at rest, increased esotropia and mild slowing of abducting saccades of the left eye. Subsequently there was gradual resolution of symptoms. One year after treatment, the patient was asymptomatic, even on exercise. He had a well-controlled esophoria and the brain stem lesion had regressed on MRI.

Comment

Chronic-isolated sixth nerve palsy1 and acute divergence weakness esotropia2, 3 are recognised presentations of brainstem glioma. Although clinically there was no limitation of abduction or slowing of abduction saccades, even after exercise, the Hess chart indicated mild left lateral rectus palsy. This was supported by the development of slowed abduction saccades following radiotherapy.

Among three previously reported cases of exercise-induced diplopia, two had cerebral or cerebellar astrocytoma and no cause was identified in the third.4, 5, 6 This contrasts with exercise-induced visual loss (Uhthoff's phenomenon) that is usually due to demyelinative optic neuropathy. Exercise-induced double vision is uncommon but is usually due to intracranial glioma.