The Guillain-Mollaret triangle in action.

The Guillain-Mollaret triangle comprises the ipsilateral red nucleus in the midbrain, the inferior olive in the medulla and the contralateral dentate nucleus in the cerebellum: together, these form the dentato-rubro-olivary pathway. Pathology in this triangle disinhibits (and so activates) the inferior olivary nucleus. The olivary nucleus then hypertrophies and its rhythmical discharges may manifest clinically as oculopalatal tremor. We describe three cases with either oculopalatal tremor or MRI evidence of olivary hypertrophy caused by vascular insults to this triangle. It is not clear why only some patients have the oculopalatal tremor. Olivary hypertrophy can be confused with demyelination if the imaging is not put into clinical context. Oculopalatal tremor may occur without olivary hypertrophy since the nucleus atrophies with time. Oculopalatal tremor does not respond to medical treatment. A better understanding of the mechanism of the discharge at a cellular level may lead to more targeted medical treatments. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/