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encephalopathy, is a late complication of HIV disease that occurs in those with very low CD4+
cell counts. Fortunately, HAD is very responsive to anti-retroviral therapy and has become
uncommon in the developed world. In the developing world, more studies are required to enable
conclusions to be made on HAD. Since the introduction of Highly Active Anti-Retroviral
Therapy (HAART) in 1996, the incidence of HAD has declined by about 50 per cent compared to
the early 1990s. Studies conducted in the pre-HAART era found that HAD was associated with
increasing age, a diagnosis of AIDS and injection drug use. The majority of cases have presented
with advanced immunosuppression with CD4+ counts <200. Since the advent of HAART,
however, more cases are presenting at higher CD4+ counts.
The clinical presentation in adults includes prominent psychomotor slowing, deficits in learning,
attention/working memory, speeded information processing, mental flexibility, and motor control.
Neuropsychological testing can demonstrate deficits in these areas. Typically, HAD progresses
slowly over several months, rather than being sudden in onset, and those affected or their families
describe a slowing of thought with loss of interest in activities previously enjoyed and a tendency
to forget details. Less commonly, psychotic behaviour may be quite florid. Diagnosis of HAD can
be made clinically, but MRI imaging or CT scanning should be considered to exclude
opportunistic lesions. The scans may be normal in the presence of HAD but generally cerebral
atrophy is present.
e) Mild neurocognitive impairment
It is difficult to come to a clear conclusion on the absolute risk and significance of mild
neurocognitive impairment in asymptomatic HIV infected individuals. Whilst some studies
comparing cognitive function in asymptomatic HIV positive persons and HIV negative persons
find no difference, others have detected a higher frequency of cross-sectional neuropsychological
test abnormalities than in seronegative controls. However, few have shown that these cognitive
impairments are progressive, or predictive of later development of dementia. The clinical
significance of new cognitive symptoms or test impairment in asymptomatic HIV infection is
uncertain because the reported neuropsychological abnormalities do not necessarily affect every
day function, may not progress, and in some individuals may improve on retesting.
Where abnormalities have been detected, they relate to timed psychomotor tasks and memory
tasks that require attention, learning and active monitoring or retrieval of information. These may
be assessed using trail making, digit symbol substitution, grooved pegboard and computerized
reaction time tests. The development of sensitive and reliable neuropsychological test batteries
now means that evolving neurocognitive impairment may be detected at a relatively early stage in
individuals at risk of HIV dementia.
Under ideal circumstances every patient should receive baseline neuropsychological assessment
when first diagnosed with HIV but there is no perfect approach. Tests vary in their sensitivity and
specificity, as well as the degree to which they are affected by other general factors such as age,
education and cultural background, premorbid neurological disease, and alcohol and drug use,
fatigue, constitutional symptoms, and mood. This is a reason for assessing cognitive ability
domains utilizing more than one test of each domain.
Overall neuropsychological evaluation may be enhanced by the results of functional testing such
as the proficiency checks that commercial pilots undertake regularly in a flight simulator. This
ICAO Preliminary Unedited Version — November 2009 III-13-8
may be particularly useful where cognitive function testing has detected mild impairments of
uncertain significance or instead of cognitive function testing in asymptomatic individuals who
are at low risk of disease progression (see Risk of Progression).
f) Simulator checks
In general, simulator checks test two main abilities, which are: learned skills, e.g. controlling an
aircraft after engine failure, flying an instrument approach with engine(s) failed, and decision
making, e.g. choosing an appropriate course of action given more than one option, and
determining the cause of a malfunction from a given set of data. Most, if not all, of the identified
types of neurocognitive deterioration can be identified by a well-designed simulator check.
Controlling a twin-engine aircraft after an engine failure following take-off or while flying an
approach are demanding psychomotor tasks and should be part of any routine simulator test.
Memory tasks are also necessary as a routine, but can be emphasized by the airline medical
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Manual of Civil Aviation Medicine 2(94)
