The permanent neurologic sequelae or posthypoxic syndromes observed most frequently are as follows: 1. Persistent coma or stupor, described above 2. With lesser degrees of cerebral injury, dementia with or without extrapyramidal signs 3. Extrapyramidal (parkinsonian) syndrome with cognitive impairment (discussed in relation to CO poisoning) 4. Choreoathetosis 5. Cerebellar ataxia 6. Intention or action myoclonus (Lance-Adams syndrome) 7. An amnesic state
If hypoperfusion dominates, the patient may also display the manifestations of watershed infarctions that are situated between the end territories of the major cerebral vessels. The main syndromes that become evident soon after the patient awakens are as follows: 1. Visual agnosias including Balint syndrome and cortical blindness (Anton syndrome) (see Chap. 21), representing infarctions of the watershed between the middle and posterior cerebral arteries (see Fig. 39-2) 2. Proximal arm and shoulder weakness, sometimes accompanied by hip weakness (referred to as a “person [man]-in-the-barrel” syndrome), reflecting infarction in the territory between the middle and anterior cerebral arteries. These patients are able to walk, but their arms dangle and their hips may be weak.
The two watershed syndromes may rarely coexist. The interested reader may consult the appropriate chapter in the text on neurologic intensive care by Ropper and colleagues for further details. There are also watershed areas in the spinal cord (Chap. 42).
Seizures may or may not be a problem, and when present are often resistant to treatment. Well-formed motor convulsions are infrequent. Myoclonus is more common and may be intermixed with fragmentary convulsions. Myoclonus is a grave sign in most cases but it generally recedes after several hours or a few days. These movements are also difficult to suppress, as noted further on.
This is a relatively uncommon and unexplained phenomenon. Initial improvement, which appears to be complete, is followed after a variable period of time (1 to 4 weeks in most instances) by a relapse, characterized by apathy, confusion, irritability, and occasionally agitation or mania. Most patients survive this second episode, but some are left with serious mental and motor disturbances (Choi; Plum et al). In still other cases, there appears to be progression of the initial neurologic syndrome with additional weakness, shuffling gait, diffuse rigidity and spasticity, sphincteric incontinence, coma, and death after 1 to 2 weeks. Exceptionally, there is yet another syndrome in which an episode of hypoxia is followed by slow deterioration, which progresses for weeks to months until the patient is mute, rigid, and helpless. In such cases, the basal ganglia are affected more than the cerebral cortex and white matter as in the case studied by our colleagues Dooling and Richardson. Instances have followed cardiac arrest, drowning, asphyxiation, and carbon monoxide poisoning.
The imaging features of the white matter disorder can be quite striking (Fig. 39-4). A mitochondrial disorder has been suggested, on uncertain grounds, as the underlying mechanism.
Prognosis of Hypoxic-Ischemic Brain Injury (See Also “Prognosis in Coma” in Chap. 16)