The Paramedian Diencephalic Syndrome (PDS) may be caused by bilateral thalamic infarcts or other lesions of the paramedian diencephalon. It can often be suspected clinically based on the pattern of clinical findings.



(1) syndrome of the basilar communicating artery of Percheron

(2) syndrome of the mesencephalic artery

(3) thalamosubthalamic infarction syndrome

(4) syndrome of the thalamoperforating pedicle of Foix and Hillemand


Main features:

(1) abrupt onset

(2) dramatic fluctuations in sensorium/symptoms

(3) hypersomnolent apathy

(4) persistent amnesic syndrome resembling Korsakoff's syndrome

(5) abnormal vertical gaze, most often with dysfunction of downward gaze


Additional findings:

(1) "subcortical" dementia with preservation of verbal IQ and a relative absence of aphasia, agnosia and verbal apraxia.

(2) dysorthographia (disturbed writing without oral language difficulties)

(3) language difficulties (confabulatory and perseveratory responses, hypophonia, hypokinetic dysarthria, aprosodia)

(4) convergence insufficiency causing difficulty reading

(5) poor learning and recall

(6) impaired comprehension of complex auditory commands


Anatomic Correlate


dorsomedial nucleus

vertical gaze abnormalities

prerubral region

hypokinetic dysarthria

basal ganglia afferents


intralaminar nuclei

fluctuating deficits

intralaminar nuclei

Figure 5, page 384


Differential diagnosis:

(1) Korsakoff's syndrome

(2) cortical syndrome (these tend to be stable while PDS shows dramatic fluctuations in symptoms)


To read more or access our algorithms and calculators, please log in or register.