We present genetically identical twin patients who experienced late-onset migraine with visual and somatosensory auras and later developed hemiplegic migraines associated with severe cortical oedema and enhancement. Both positron emission tomography and electroencephalography showed an increase in activity contralateral to the hemiplegic side. Brain biopsy during the attack showed reactive astrogliosis and microgliosis. Mutations in CACNA1A, ATP1A2, SLC1A3 and NOTCH3 were ruled out by sequencing. This report shows the clinical and genetic evaluation of a severe form of familial hemiplegic migraine as well as the evolution of the imaging changes.