Objectives We report a case of Miller-Fisher syndrome presenting initially with thunderclap headache.

Case A 77 year old male with a history of type 2 diabetes mellitus, hypertension, depression and previous right pontine stroke, presented to our hospital with thunderclap headache and syncope. He reported a brief, non-bloody, diarrhoeal illness five weeks prior but he had otherwise been well. There was recurrent thunderclap headache over the following 24 hours with subsequent vomiting and syncope. He was diagnosed with vagal-induced sinus pause causing syncope. Plain CT brain and CT angiogram were unremarkable. Over the following 48 hours, the patient developed ocular signs, which progressed to complete ophthalmoplegia and complete ptosis. CSF examination was unremarkable (protein 0.30 g/L, acellular). MRI brain, including post-gadolinium enhanced imaging of orbits and cavernous sinus, was unremarkable. Three days after presentation, his reflexes began to diminish in the lower limbs and he developed heel-shin ataxia. The presumptive diagnosis was Miller Fisher syndrome and he was commenced on intravenous immunoglobulin (2 g/kg over three days). Supportive tests returning after initiation of treatment were positive serum anti-GQ1B IgG antibodies and positive stool culture for Campylobacter jejuni. Despite this, the patient’s severe headaches persisted, non-responsive to opiod analgesia and non-steroidal anti-inflammatory agents. Repeat CSF examination was unremarkable, with an opening pressure of 13 cm H₂O. Twelve days after initial onset of headache, the patient was trialled on oral nimodipine 60  TDS, with resolution of headache over the following 12 hours.

Conclusions Although not radiographically confirmed, we postulate the headache may have been due to reversible cerebral vasoconstriction syndrome (RCVS), given the characteristics of the headache and dramatic response to nimodipine. Although headache is infrequently observed in Miller Fisher syndrome, the exact aetiology is unclear and there has been no previously reported association with RCVS.