The neurologic examination may disclose whether the disease is supratentorial, subtentorial, or metabolic. Hyperventilation usually reflects metabolic or pulmonary disease but sometimes reflects upper pontine or midbrain damage. Pupils are dilated in anoxia or 3rd nerve compression but remain normally reactive in most metabolic diseases, hemispheric disease, and psychogenic unresponsiveness. Oculovestibular responses to cold caloric stimulation show bilateral tonic conjugate deviation toward the ear irrigated with cold water in hemispheric depression. Oculovestibular responses are absent or dysconjugate in brain stem impairment and show only minimal nystagmus or random movements in psychogenic unresponsiveness.
Hemispheric lesions produce hemiplegic motor responses to painful stimuli.
Motor signs and reflexes remain normal in psychogenic unresponsiveness. Characteristically, when supratentorial lesions cause stupor or coma, neurologic signs and symptoms first indicate involvement of one cerebral hemisphere. Then, because the mass enlarges and pressure changes cause brain tissues to shift, signs of progressive rostral-caudal deterioration develop, indicating involvement first of the diencephalon and finally of the brain stem. When unconsciousness results from a primary brain stem lesion, pupillary and oculomotor signs are abnormal from the start. Laboratory studies in patients with acute stupor or coma of unknown cause begin with blood glucose measurements.