Handbook of Solvents - George Wypych - ChemTech - Ventech!

1330 Jenni A Ogden
form poorly on the tests. For example, if an individual was unable to remember any new visual
stimuli (an extremely rare condition), when given a memory test where the worker is
shown 50 photographs of unknown faces, and is then shown fifty pairs of faces and must
choose from each pair the face which he or she has previously seen, he or she should obtain
a score of approximately 50% (chance level) correct. If the score was considerably worse
than that, malingering or exaggerating might reasonably be suspected. Tests which measure
reaction or response times for increasingly complex tasks are also difficult to malinger
successfully on as humans are not good at estimating response times in milliseconds, or
even seconds.
A diagnosis of Type 2 OSN is based on score deficits (measured by the number of
Standard Deviations (SD) below the worker’s estimated premorbid ability level) on those
tests commonly impaired by OSN. At least three neuropsychological test scores must fall
more than 1 SD below the scores expected for that worker to be categorized as mild Type 2
OSN, three test scores below 2 SDs for moderate Type 2 OSN, and three or more test scores
more than 3 SDs below the expected levels for moderate-severe Type 2 OSN. 4 The presence
and severity of typical psychological symptoms are also taken into account, and in clear
cases in which either psychological or cognitive symptoms are very dominant, this information
informs a decision regarding Type 2A or Type 2B OSN. Whilst psychological symptoms
are the reason most workers come to the attention of health professionals, because of
the difficulty of measuring the severity of these symptoms and of attributing them to a neurological
syndrome, only workers who demonstrate neuropsychological impairments on
testing are positively diagnosed with OSN. The New Zealand experience has, however,
demonstrated that the vast majority of workers with significant solvent exposure histories
and severe psychological problems do demonstrate neuropsychological impairments, and
vice versa. 10
20.2.5 DO THE SYMPTOMS OF TYPE 2 OSN RESOLVE?
Occasionally after an extended period away from solvents (perhaps 6 months to a year), the
worker’s psychological symptoms resolve, and on re-testing it is found that his or her
neuropsychological impairments have also resolved. In these cases the classification is
changed to Type 1 OSN (resolved). A recent New Zealand study re-assessed 21 men with
confirmed cases of OSN 6 to 41 (mean 27) months after ceasing exposure. 17 An exposure
score was calculated for each worker by using the formula AxBxC, where A = years of solvent
exposure, B = a weighting for the occupational group (where boat builders, spray
painters and floorlayers had the highest weighting of 3), andC=aweighting reflecting the
lack of safety precautions taken by the worker relative to other workers in the same job.
Neuropsychological and psychological symptoms at the initial and follow-up assessments
were categorized as mild, moderate or moderate-severe (using the system described above)
by a neuropsychologist blind to the men’s initial diagnosis or exposure history. Twelve men
(57%) showed no improvement (or in one case a slight worsening) on cognitive and psychological
assessment. Seven men showed some improvement on cognitive tests (but not to
“normal” levels), only three of whom also improved on psychological assessment. A further
two men showed an improvement in psychological functioning only. Men given a more severe
OSN diagnosis at their initial assessment were more likely to improve than men with
milder symptoms at the time of their first assessment. Possible explanations for this include
the likelihood that some of the more severe symptoms on initial assessment were exacerbated
by the lingering effects of acute solvent exposure, or that those with mild OSN were