Elsevier

Ophthalmology

Volume 106, Issue 7, 1 July 1999, Pages 1287-1291
Ophthalmology

Positron emission tomography scan in cortical visual loss in patients with organophosphate intoxication

https://doi.org/10.1016/S0161-6420(99)00710-1Get rights and content

Abstract

Objective

To determine the cerebral metabolism of patients with cortical visual loss.

Design

Two observational case studies.

Testing

Two patients who survived acute organophosphate poisoning with respiratory failure experienced severe visual loss despite relatively normal ophthalmic examination results. Magnetic resonance imaging of the brain revealed no abnormality of the visual system in either patient. Positron emission tomography (PET) was performed in these 2 patients and in 12 normal subjects with fluorine-18 fluorodeoxyglucose (FDG) as a tracer to measure cerebral glucose metabolism for the estimation of neurologic deficit in the visual cortex.

Main outcome measures

The FDG uptake values were measured as nanoCurie per cubic centimeters of tissue (nCi/cc). The relative uptake index in visual cortex was computed as the ratio of uptake of FDG in each region of visual cortex to that of cerebellum (regional visual cortex/cerebellum).

Results

Hypometabolism was observed in the visual cortex of both patients. The relative uptake index of FDG in visual cortex (visual cortex/cerebellum) was significantly decreased in those patients compared with normal subjects.

Conclusions

In patients with cortical visual loss, conventional neuroimaging techniques can fail to visualize damage that can be detected by PET scanning, and PET analysis may be helpful in estimating the metabolic deficit of visual cortex and in establishing the organic nature of cortical visual loss in these patients.

Section snippets

Case 1

A 37-year-old woman who had experienced blurred vision and vertical nystagmus for approximately 1 year visited our outpatient department. She had been attacked by her boyfriend with an injection of 15 ml O-ethyl-O-p-nitrophenyl phenylphosphonate over her left buttock area on July 1995. She had been sent to a local hospital and received atropine injection as an antidote. She was transferred to our hospital. Endotracheal intubation with ventilatory support was given immediately. Atropine and

Results

In case 1, the FDG-PET images showed remarkably decreased FDG uptake in the visual cortex (Fig 3B). The metabolic values (visual cortex/cerebellum ratio of FDG uptake) for the occipital visual areas were also lower than the mean metabolic values of the visual cortex in normal volunteers (Table 1).

In case 2, the metabolic images revealed hypometabolism in the visual cortex (Fig 3C). The metabolic values for the occipital visual cortex were decreased in comparison with the normal reference values

Discussion

Organophosphate insecticides act as irreversible cholinesterase inhibitors. The inhibition of cholinesterase activity leads to the accumulation of acetylcholine at synapses, causing overstimulation and subsequent disruption of transmission in both the central and the peripheral nervous systems. The clinical manifestations of acute organophosphate poisoning include overstimulation of muscarinic, nicotinic, and central nervous system receptors.7 Muscarinic overstimulation may show miosis;

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