Technetium-99m HM-PAO SPECT in patients with delayed neurologic sequelae after carbon monoxide poisoning

Combined treatment of methylprednisolone pulse and memantine hydrochloride prompts recovery from neurological dysfunction and cerebral hypoperfusion in carbon monoxide poisoning: a case report

A 49-year-old healthy man developed sudden unconsciousness under inadequate ventilation. Blood gas analysis showed carboxyhemoglobin of 7.3%. After normobaric oxygen therapy, he recovered completely 7 days later. At 3 weeks after carbon monoxide (CO) exposures, memory and gait disturbances appeared. Neurological examination revealed Mini-Mental State Examination (MMSE) score of 5 of 30 points, leg hyper-reflexia with Babinski signs, and Parkinsonism. Brain fluid-attenuated inversion recovery imaging disclosed symmetric hypointense lesions in the thalamus and the globus pallidus, and hyperintense lesions in the cerebral white matter. Brain single-photon emission tomography (SPECT) scanning with (99m)Technesium-ethyl cysteinate dimer displayed marked hypoperfusion in the cerebellum, the thalamus, the basal ganglia, and the entire cerebral cortex. He was diagnosed as CO poisoning and treated with hyperbaric oxygen therapy. The neurological deficits were not ameliorated. At 9 weeks after neurological onset, methylprednisolone (1000 mg/day, intravenous, 3 days) and memantine hydrochloride (20 mg/day, per os) were administered. Three days later, MMSE score was increased from 3 to 20 points. Neurological examination was normal 3 weeks later. Brain SPECT exhibited 20% increase of regional cerebral blood flows in the cerebellum, the thalamus, the basal ganglia, and the entire cerebral cortex. These clinicoradiological changes supported that the treatment with steroid pulse and memantine hydrochloride could prompt recovery from neurological dysfunction and cerebral hypoperfusion. Further clinical trials are warranted whether such combined therapy can attenuate neurological deficits and cerebral hypoperfusion in patients with CO poisoning.

Toxic leukoencephalopathies

Leukoencephalopathy is a syndrome of neurologic deficits, including alteration of mental status, caused by pathologic changes in the cerebral white matter. The term, toxic leukoencephalopathy, encompasses a wide variety of exposures and clinical presentations. The diagnosis in these Frontiers in Clinical Neurotoxicology syndromes is made by careful attention to the history, clinical features, and radiologic findings. This article details three of the best-defined toxic leukoencephalopathies: delayed posthypoxic leukoencephalopathy, including delayed neurologic sequelae after carbon monoxide poisoning; heroin inhalation leukoencephalopathy; and posterior reversible encephalopathy syndrome.

Hyperbaric oxygen and carbon monoxide poisoning: a critical review

CO is likely to be the most common cause of poisoning worldwide and often results in persistent neuropathologic and cognitive sequelae. While the displacement of oxygen from hemoglobin by CO has overshadowed the myriad mechanisms by which CO causes injury, mere oxygen displacement has endured as the etiology of CO poisonings and perpetuated a cascade of misdiagnosis, misunderstandings and confusion regarding how and when to treat CO poisoning. Hyperbaric oxygen benefits the brain more than normobaric oxygen by, e.g. improving energy metabolism, preventing lipid peroxidation and decreasing neutrophil adherence. Randomized controlled trials have definitively shown hyperbaric oxygen as the only efficacious therapy for acute CO poisoning if delayed neurological sequelae are to be minimized. Normobaric oxygen should not be used between multiple hyperbaric oxygen treatments as this can contribute to toxicity. Hyperbaric oxygen seems to also have potential in the delayed treatment of CO poisoning using multiple treatments of low dose of oxygen; however, oxygen dosing issues are not yet fully understood for either acute or delayed treatment. It would behoove medical decision-makers to embrace this important tool and make it more accessible as well as helping to disseminate to the medical community what is now known from the available literature.

Affective outcome following carbon monoxide poisoning: a prospective longitudinal study

OBJECTIVE

To longitudinally assess the prevalence of depression and anxiety following carbon monoxide (CO) poisoning and to assess the contributions of mode of poisoning (accidental versus suicide attempt), cognitive sequelae, and oxygen dose (hyperbaric oxygen versus normobaric oxygen) to depression and anxiety.

BACKGROUND

CO is the most common cause of poisoning in the United States and may result in neuropathologic changes and cognitive and neurologic sequelae, yet little is known regarding affective outcomes.

METHOD

We prospectively assessed affect in 127 CO-poisoned patients. Self-report inventories of depression and anxiety were administered at 6 weeks and at 6 and 12 months post CO poisoning. The primary outcome was prevalence of depression and anxiety at 6 weeks. To determine the effect of mode of poisoning, cognitive sequelae, and oxygen dose, odds ratio estimates were calculated at all three times using logistic regression.

RESULTS

Depression and anxiety were present in 45% of patients at 6 weeks, 44% at 6 months, and 43% at 12 months. Patients with suicide attempt and cognitive sequelae had higher prevalence of depression and anxiety at 6 weeks. At 12 months, there were no differences in depression or anxiety regardless of mode of poisoning, presence of cognitive sequelae, or oxygen dose.

CONCLUSIONS

CO poisoning results in significant depression and anxiety that persist to at least 12 months. Patients with cognitive sequelae and suicide attempt had a higher rate of depression and anxiety at 6 weeks but not at 12 months. Clinicians need to be aware of affective morbidity following CO poisoning and remain vigilant about CO prevention.

Carbon monoxide poisoning

Carbon monoxide (CO) poisoning is common and frequently unrecognized since the signs and symptoms are relatively nonspecific. CO poisoning causes tissue hypoxia. Additionally, various animal studies have demonstrated that CO interferes with myoglobin, P450, and other enzyme function; causes lipid peroxidation through neutrophil activation; produces oxidative stress manifested by peroxynitrate deposition in endothelium; binds to cytochrome aa3, disrupting intracellular oxygen utilization; can cause neuroexcitotoxicity; and contributes to hippocampal cellular death through apoptosis. Emergency treatment for CO poisoning is 100% oxygen. Hyperbaric oxygen therapy (HBO2) is accepted in CO poisoning, although data from randomized clinical trials regarding the efficacy of HBO2 in CO poisoning is conflicting. CO poisoning, even when treated with supplemental oxygen can leave the patient with permanent neurocognitive or affective problems. Unfortunately, there appears to be no marker or constellation of signs or symptoms at presentation that predicts long-term outcome following CO poisoning. Given the neurocognitive sequelae following CO poisoning, increased awareness and prevention of CO poisoning is imperative.

Neurospect in neurotoxic chemical exposure demonstration of long-term functional abnormalities

Patients who had experienced well-documented neurotoxic exposure months or years earlier were evaluated. Seventy-two right-handed adults who claimed continuing abnormalities of cognitive and memory function were examined after Xenon-133 inhalation and i.v. HMPAO. Single photon emission computed tomography (SPECT) results were statistically compared with age-matched controls. Bilateral, often asymmetrical, impairment of perfusion was found, mostly in the frontal, temporal, and parietal lobes. This hypoperfusion was predominantly left-sided in young patients and predominantly right-sided in the elderly. Abnormalities were found months and years after neurotoxic exposure had ceased. Our findings suggest that NeuroSPECT can provide evidence of impaired cerebral function and may therefore help to further define neurotoxic exposure and its chronic effects.

A neuro-ophthalmologist's perspective on neuroradiology

The practice of neuro-ophthalmology includes evaluating patients for visual signs and symptoms for neurological causes. Responsible lesions are often small and in places not well imaged on routinely ordered brain imaging studies. To achieve a proper diagnosis, the clinician must have a close working relationship with the radiologist to choose the appropriate imaging study and to correctly focus the study based on clinical findings.

Physiologic functional imaging in "functional" visual loss

Neuroimaging with nuclear medicine techniques permits assessment of brain function by measurement of metabolism or blood flow. Such studies complement the anatomic information derived from computed tomography (CT) or magnetic resonance imaging (MRI). We describe two patients with occipital lesions who were initially diagnosed with functional visual loss. Neither CT scan nor MRI adequately demonstrated the source of visual dysfunction; however, single proton emission tomography (SPECT) scanning in a patient with carbon monoxide poisoning and positron emission tomography (PET) scanning in a patient with post-hypoxic delayed encephalopathy were helpful in confirming the organic substrate of their visual impairment. Functional imaging techniques such as SPECT and PET should be considered in patients with suspected cortical visual loss and normal CT or MR scans.