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Acute CO Poisoning:

Comparing High-tech Scanning and Neuropsychological Approaches:

Study Title:
MRI, quantitative MRI, SPECT, and neuropsychological findings following carbon monoxide poisoning

Gale, S.D., Hopkins, R.O., Weaver, L.K., Bigler, E.D., Booth, E.J., Blatter, D.D.


Brain Injury, 13 (4), pgs. 229-243.

BACKGROUND: Carbon monoxide (CO) poisoning has been shown to result in neuropathologic changes and cognitive impairments due to anoxia and other related biochemical mechanisms.

METHODS: The present study investigated brain-behaviour relationships between neuropsychological outcome and SPECT, MRI, and Quantitative magnetic resonance imaging (QMRI) in 21 patients with CO poisoning.

RESULTS: Ninety-three per cent of the patients exhibited a variety of cognitive impairments, including impaired attention, memory, executive function, and mental processing speed. Ninety-five per cent of the patients experienced affective changes including depression and anxiety. The results from the imaging studies revealed that 38% of the patients had abnormal clinical MRI scans, 67% had abnormal SPECT scans, and 67% had QMRI findings including hippocampal atrophy and/or diffuse cortical atrophy evidenced by an enlarged ventricle-to-brain ratio (VBR). Hippocampal atrophy was also found on QMRI. SPECT and QMRI appear to be sensitive tools which can be used to identify the neuropathological changes and cerebral perfusion defects which occur following CO poisoning. Cerebral perfusion defects include frontal and temporal lobe hypoperfusion. Significant relationships existed between the various imaging techniques and neuropsychological impairments.

CONCLUSION: The data from this study indicate that a multi-faceted approach to clinical evaluation of the neuropathological and neurobehavioural changes following CO poisoning may provide comprehensive information regarding the neuroanatomical and neurobehavioural effects of CO poisoning.

Location of Authors:
LDS Hospital, Salt Lake City, Utah 84143, USA

More on Methods: Archival data from 21 patients with moderate to severe CO poisoning were used for this study. All patients had an independently confirmed diagnosis of CO poisoning by a physician and were referred for brain imaging and comprehensive neuropsychological evaluations. There were nine females and 12 males, all were treated with 100% normobaric oxygen or hyperbaric oxygen (HBO or NBO therapy) following the poisoning (4 patients were intubated). The patients had a mean age of 39 +/-7 years (range 27-52 yrs.) with a mean educational level of 15 +/-2.9 years (range 8-20 yrs). The time from CO exposure to MRI scan was a mean of 21.3 +/-14.3 months (range 4-45 mo.) and time from exposure to SPECT scan was 20.6 +/-12.6 months (range 5-41 mos. The MRI and SPECT studies occurred withing 2 days of each other, in the majority of patients (19 of 21).

COHb was measured in 8 patients, the other 13 did not have COHb levels done, but were exposed to CO as determined by documented high environmental CO levels due to faulty furnaces. In 3 of these 13 cases, other individuals died due to exposure to CO; 5 of the patients were staying in a home where ambient CO level was measured at 2400 ppm, and the other 5 patients had documented defective furnaces which were producing significantly elevated environmental CO levels. The mean COHb was 26.0%, and 38% of patients lost consciousness (8 of 21). All patients in this group had accidental exposure to CO. CO poisoned patients were excluded from this study if they were less than 16 years old, had a prior head injury, or neurological condition, and if they did not receive cranial MRI and SPECT studies in addition to neuropsychological studies.
The following areas of cognition were examined: Intellectual functioning (WAIS-R), memory (unfortunately the obsolete WMS-R was used), attention / concentration (WMS-R), visual-spatial (WAIS-R), visual-motor integration / mental processing speed (Digit Symbol, Trail-making A & B, Halstead-Reitan Neuropsychological Test Battery), executive function (Category Test, Wisconsin Card Sorting Test), neuropsychological impairment, and psychological testing (Beck depression Inventory).

More on Results: 76% of the patients had significant memory impairments, 75% had impaired executive function, 57% had slow mental processing speed, and 45% experienced impaired attention. Memory performance for these subjects was significantly lower than would be expected from a population with an average educational level of almost 16 years and an estimated pre-morbid IQ of 110. The patients' mental processing speed was below average on Trail-making test B, where the average T-score was 41, where a T-score of 40 is 16th%ile. Psychologic testing (BDI, BAI, MMPI, SCL-90-R) indicated affective disturbance in 20 of 21 patients (95%).

To Especially Note:

  • A high percentage of CO poisoned patients showed residual memory and cognitive (executive function, mental processing speed, attention/concentration) deficits.
  • A large percentage of CO poisoned patients demonstrate clinically significant mood disorder 1 year post-exposure.
  • Unconsciousness is not necessary to produce the above impairments and affective disorders.
  • QMRI is sensitive to the neuropathological effects of CO poisoning, including hippocampal atrophy and increased VBR secondary to diffuse cortical atrophy.
  • SPECT scans show CO-induced changes in brain function as seen by decreased cerebral perfusion.
  • This study corroborates past research that found neuropsychological impairments correlate with neuroimaging findings.

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