Cognitive functioning in patients with suspected chronic toxic encephalopathy: evidence for neuropsychological disturbances after controlling for insufficient effort
- 1Medical Spectrum Twente Hospital, Enschede, the Netherlands
- 2Academic Medical Centre, Departments of Neurology and Psychonomics, University of Amsterdam, the Netherlands
- 3Departments of Psychology, Neurology and Neuropsychology, University of Leiden, the Netherlands
- 4Academic Medical Centre, Netherlands Centre for Occupational Diseases, Amsterdam, the Netherlands
- 5Department of Neuropsychology, University of Groningen, the Netherlands
- Correspondence to: Dr M van Hout Department of Psychology, Medical Spectrum Twente Hospital, PO Box 50000, NL-7500 KA Enschede, the Netherlands; m.vanhout{at}ziekenhuis-mst.nl
- Received 8 June 2004
- Accepted 12 September 2005
- Revised 8 September 2005
Abstract
Objectives: Chronic toxic encephalopathy (CTE) caused by long term occupational exposure to organic solvents is still a controversial disorder. Neuropsychological testing is the cornerstone for diagnosing the syndrome, but can be negatively influenced by motivational problems. In this nationwide study, we investigated the neuropsychological functioning and psychological symptoms of a large group of patients with suspected CTE, and ruled out alternative explanations for their complaints, including suboptimal performance due to insufficient effort.
Methods: We studied participants with suspected CTE (n = 386) who were referred for further diagnosis to the Netherlands Centre of Occupational Diseases in the period 1998–2003 and who had completed the entire diagnostic protocol. Patients were excluded if there was the slightest suspicion that test performance had been negatively influenced by insufficient effort (n = 221), or if comprehensive assessment identified an alternative diagnosis (n = 80). Insufficient effort was defined by a combination of three indices. The neuropsychological test scores of the patient group (n = 85) were compared with those of a control group of building trade workers matched for sex, age, and educational level (n = 35).
Results: The patient group had significantly more psychological complaints and performed significantly worse than the control group on tests of speed of information processing and memory and learning. However, only a small percentage of the patients had clearly abnormal scores for cognitive speed (9%) or memory (8%). Attention, verbal abilities, and constructional functions were not disturbed. Exposure duration and cognitive complaints were significantly correlated, whereas the correlation between exposure duration and neuropsychological domain scores was not significant.
Conclusions: Insufficient effort was present in a substantial part of the patient group. After minimising the likelihood that insufficient effort negatively influenced neuropsychological scores, we still found neuropsychological deficits in speed of cognitive processing and memory; however, these scores were clearly abnormal only in a minority of patients with suspected CTE. Screening instruments should focus on these domains.
- ASTM, Amsterdam Short Term Memory Test
- CNS, central nervous system
- CTE, chronic toxic encephalopathy
- NCTB, Neurobehavioural Core Test Battery
- NES2, Neurobehavioral Evaluation System
- RMT, Recognition Memory Test
- TOMM, Test of Memory Malingering
- chronic toxic encephalopathy
- malingering
- neuropsychological tests
- solvents/toxicity
- occupational diseases
- cognitive disorders
Footnotes
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Competing interests: none
