Sir,

Latanoprost is a phenyl-substituted isopropyl ester of prostaglandin F2a, effective in low-tension glaucoma (LTG), lowering intraocular pressure (IOP), improving pulsatile ocular blood flow, and increasing ocular perfusion pressure.1, 2 Adverse topical effects such as anterior uveitis, cystoid macular oedema, conjuctival hyperaemia, and pigmentation of intra- and extraocular structures have been reported.3 Systemic side effects are rare but may occur such as facial rash, cardiovascular effects,4 and headaches.5

We report a favourable side effect of latanoprost in a woman with LTG. She reported complete cessation of her migraines after the use of latanoprost. She remained free of episodes of migraines for more than 1 year. Satisfactory challenge and rechallenge were performed.

Case report

A 57-year-old Caucasian woman, with a history of frequent migraines (every other day to once a week), low blood pressure (LBP), and peripheral vasospasm was referred with suspected glaucoma. Her best-corrected visual acuity was 6/6 in either eye. Clinical examination revealed findings consistent with a diagnosis of LTG. The patient was commenced on latanoprost monotherapy.

The IOP was reduced more than 30% from baseline. In addition the patient happily mentioned that as using latanoprost she had not experienced any new episodes of migraines although these were very frequent before she started the medication. The patient remained free of episodes of migraine for more than 1 year. There were no work, nutritional, or environmental factors that had changed during this year.

She subsequently developed ocular discomfort with latanoprost and her topical treatment was changed to brinzolamide. She suffered four episodes of migraine over a period of 1 month while she was using brinzolamide. She requested to have her topical therapy changed to latanoprost. No new episodes of migraines occurred when she reverted back to using latanoprost.

The patient later carried out a challenge and rechallenge on her own accord and her migraines once again recurred when she stopped latanoprost.

Comment

LTG is a distinct entity of primary open-angle glaucoma.1 LBP and peripheral vasospasm are established risks factors for LTG.1, 6 Latanoprost is effective in LTG, lowering IOP, improving pulsatile ocular blood flow, and increasing ocular perfusion pressure.1

Many theories of migraine pathogenesis have been proposed, but the exact mechanism is still not understood. Usually the attack is started by one or more triggers.7

According to the literature,5 latanoprost may rarely cause headaches in normal, with no peripheral vasospasm, subjects. However it has never been known to aggravate headaches in known migraine sufferers.

It is known that prostaglandin F2a causes relaxation of the ciliary muscle which increases uveoscleral outflow.2, 8 This may relieve the ciliary muscle spasm which can cause pain referred to the brow and as a result can cause migraine-type headache.

In a comparative study involving brain magnetic resonance imaging,9 patients with LTG were found to have a greater extent of cerebral infarcts and corpus callosum atrophy. This may imply a greater degree of neuronal degeneration, possibly on an ischaemic basis in LTG. It is known10 that in the human ophthalmic artery, endothelium-derived nitric oxide, and endothelin are very potent modulators of vascular tone, suggesting that they play an important role in the regulation of local blood flow in the eye.

Prostaglandin F2a is a known vasoconstrictor.4 Systemic use of prostaglandin F2a has been implicated in cardiac arrhythmias and vasospastic angina.4, 11 Sumatriptan, the most extensively investigated antimigraine drug,7 is a known vasoconstrictor.

Although the plasma half-life of local applied latanoprost is short we postulate that the main mechanism that may have caused cessation of the migraines is via a slight systemic vasoconstriction.

Migraine relief after the use of latanoprost in patients with LTG has not been previously described. However, a prospective study with large series of patients and controls may be necessary in order to determine this favourable side effect.