Magnetic Resonance Imaging Findings on Carbon Monoxide Intoxication

Carbon monoxide intoxication: an updated review

Carbon monoxide (CO), a highly toxic gas produced by incomplete combustion of hydrocarbons, is a relatively common cause of human injury. Human toxicity is often overlooked because CO is tasteless and odorless and its clinical symptoms and signs are non specific. The brain and the heart may be severely affected after CO exposure with carboxyhemoglobin (COHb) levels exceeding 20%. Damage occurs because the affinity of hemoglobin for CO is 210 times higher than for O(2). Hypoxic brain damage predominates in the cerebral cortex, cerebral white matter and basal ganglia, especially in the globus pallidus. Diagnosis requires clinical acumen and a high index of suspicion, combined with epidemiological data, clinical examination, analysis of ambient air CO and patient COHb levels; also required are cardiology evaluation including ECG as well as neurological evaluation including brain imaging (CT and/or MRI, MR spectroscopy), and neuropsychological testing. Although immediate O(2) breathing is sometimes an adequate treatment, hyperbaric oxygen therapy (HBO) is favored. Subsequently, only symptomatic therapy is available for the long-term sequelae of CO poisoning.

Troubles cognitifs dus à l’intoxication oxycarbonée: étude neuropsychologique et IRM de 5 cas

INTRODUCTION

Carbon monoxide (CO) poisoning has been shown to result in cognitive impairments. These disorders have rarely been reported. The present study aimed to evaluate these disturbances in five patients with a neuroanatomical study.

METHODS

There were two men and three women with an average of 25 years old. Patients were explored several months after acute CO poisoning. Neuropsychological testing was administered to assess memory, intellectual, executive, visual-spatial and constructional functions, language, praxis and gnosis. Cerebral magnetic resonance imaging (MRI) was performed in all patients using axial, sagittal and coronal slides with T1 and T2 weighted and flair images. None of the subjects had hyperbaric oxygen. They received 7, 5 mg bromocriptine per day.

RESULTS

All patients presented cognitive disorders including marked impairment in long term memory with a severe defect in recall performance in comparison to recognition memory. Visual memory was more affected than the verbal one. There were also moderate disturbances in intellectual, executive, visual-spatial and constructional functions. One patient presented alexia agraphia, severe visual disturbances, constructional and dressing apraxia. Four patients had depression and one psychic akinesia. Cerebral MRI studies revealed that all patients had bilateral pallidal necrosis, bilateral hippocampal and moderate cortical atrophy. Fornix atrophy was found in 2 patients and corpus mammillary atrophy in 3 patients. Others lesions were also found: bilateral cerebellar in two cases and cortical in three cases. Treatment with bromocriptine was effective in three cases. There was no improvement in the patients treated 14 months and 5 years following CO poisoning.

CONCLUSION

Neuropsychological impairments in CO poisoned subjects include memory, intellectual, executive, and visuospatial defects. In addition to pallidal necrosis, which is a typical feature of CO poisoning, hippocampal and cortical atrophy are often present. Bromocriptine can improve the cognitive disorders.

Supervisory attentional control following carbon monoxide poisoning

This study tested the hypothesis that carbon monoxide poisoning would produce a deficit of attentional control, the supervisory attention system, as indexed by attention switching and attentional scheduling, and that routine attentional orienting would be unaffected. Seventy-three cases of carbon monoxide poisoning were assessed at 3 days and 1 month post poisoning on tasks of attentional orienting, and tasks of the supervisory attention system. The results were compared to a group of 53 healthy community participants. A deficit of the supervisory attentional system was documented on a task of attention switching in survivors of both deliberate and accidental CO poisoning, leaving attentional scheduling intact. There was no deficit of attentional orienting in the current study. Alteration of consciousness was found to predict subsequent supervisory attention system impairment in correlation analyses, and the deficit was persistent for a 1 month follow-up period.

Brain CT and MRI findings after carbon monoxide toxicity

The neuropathologic sequelae of carbon monoxide (CO) toxicity have been well described in postmortem examinations. Globus pallidus damage as well as diffuse white matter lesions and encephalopathic changes occur. Brain CT has provided imaging correlates to the premortem changes. MRI is more sensitive and provides more specificity. Cerebral edema changes may occur early with subsequent demonstration of globus pallidus lesions and white matter changes. Globus pallidus lesions in many cases do not correlate directly to clinical status and outcome; however, the presence of diffuse white matter disease is a more reliable index of both. These changes are seen in patients in both accidental exposures to CO and in suicide attempts.

Neuroimaging characteristics in carbon monoxide toxicity

Neuroimaging studies for 18 patients carrying carbon monoxide toxicity as a discharge diagnosis were reviewed. The most common positive findings were low-density lesions in the globus pallidus (7/18, 39%) and deep white matter changes (5/18, 28%). Six computed tomography head scans showed no acute changes. Advanced age, method of exposure (intentional vs accidental), and severity of carboxyhemoglobin level did not predict neuroradiological or clinical outcomes. Early neuroimaging could not be used to predict clinical courses (death or coma vs discharge to either an institution or a home) in the patient population studied.