A hidden mesencephalic variant of central pain.

BACKGROUND: Central post-stroke pain (CPSP) can arise after lesions anywhere in the central somatosensory pathways, essentially within the spinothalamic system (STS). Although the STS can be selectively injured in the mesencephalon, CPSP has not been described in pure midbrain infarcts. METHODS: Out of more than 300 CPSP consecutive cases, we describe five patients who developed definite neuropathic pain following lesions circumscribed to the postero-lateral mesencephalon. RESULTS: The mesencephalic lesion responsible for pain was always haemorhagic and always involved the spinothalamic tract (STT), as demonstrated by suppressed laser-evoked potentials in every case, with or without preserved lemniscal function. In 3 cases the midbrain injury could be ascribed to trauma, presumably from the cerebellar tentorium. Due to the paucity of sensory symptoms, the pain was considered as 'psychogenic' in two of the patients until electrophysiological testing confirmed STT involvement. CONCLUSION: Postero-lateral midbrain lesions should be added to potential causes of CPSP. Because pain and spinothalamic deficits may be the only clinical sign, and because small lateral midbrain lesions may be difficult to trail with MRI, mesencephalic CPSP can be misdiagnosed as malingering or psychogenic pain for years.