Second edition

04.qxd 3/10/08 9:33 AM Page 145
difficult. ‘Insight’, a much belabored term, refers here not
to some sophisticated level of psychological understanding,
but rather simply to whether or not the patient recognizes
that the hallucination is ‘not real’. Sometimes simple
observation will enable one to determine whether the
patient experiences the hallucination as ‘real’: for example,
should a patient report seeing a dog in the room and then
reach down to pat it, one may reasonably assume that the
patient has no insight into the hallucinatory nature of the
experience. In doubtful cases, further inquiry may be
required. Although one might simply ask whether or not
the patient thinks the ‘dog’ is ‘really’ there in the room,
such questions may offend some patients, and a more
diplomatic approach is often better accepted. Thus, one
might say, in an off-handed way, ‘I don’t see it. Could you
tell me where it is?’ In cases where insight has been preserved,
the patient might respond, ‘Oh, there’s not a dog
here. I must be seeing things.’ Conversely, in cases where
insight has been lost the patient might point emphatically
to a corner of the room and say ‘It’s right over there. Can’t
you see it?’ In cases of hallucinations where insight has
been lost, the syndromal diagnosis of psychosis is reasonable,
and should be pursued as in Section 7.1. In cases of
isolated hallucinations occurring with preserved insight,
however, the diagnosis should proceed as described below.
In determining the cause of isolated hallucinations
occurring with preserved insight, the differential is different
for each of the different kinds of hallucinations, and
thus each type is discussed in turn, beginning with visual
hallucinations, and proceeding to auditory, tactile, olfactory,
and, finally, gustatory hallucinations.
Visual hallucinations are by far the most common type,
and of the various causes of these, medications and intoxicants
stand out. Of the medications capable of causing
hallucinations, by far the most common are dopaminergic
agents when used in the treatment of Parkinson’s disease.
After five or more years of treatment with levodopa, for
example, visual hallucinations occur in a little over onefifth
of all patients (Friedman and Sienkiewicz 1991;
Graham et al. 1997). The hallucinations themselves may, at
times, be quite elaborate: in one case (Graham et al. 1997)
a patient had ‘hallucinations of miniature people and
domestic animals . . . the figures were non-threatening,
laughed and talked among themselves, and had a male
leader who organized them into purposeful activities’. It is
important to note that although parkinsonian patients
with levodopa-induced visual hallucinations retain insight
initially, over many years insight tends to be lost and the
syndrome of psychosis emerges (Goetz et al. 2006). The
other medications listed in Table 4.7 are far less likely to be
at fault.
Of the intoxicants capable of causing hallucinations, the
aptly named hallucinogens immediately stand out. Of
note, in this group, one of the earliest descriptions was provided
by the eminent neurologist S. Weir Mitchell, who, in
1896, reported his own experiences with mescaline.
Although the hallucinogen-induced hallucinations are, in
4.30 Hallucinations and delusions 145
most cases, fairly simple, for example geometric forms,
they may sometimes be complex (e.g. with lysergic diethylamide
[LSD] [Bercel et al. 1956]). Hallucinogen-induced
visual hallucinations may also occur as ‘flashbacks’,
wherein long after hallucinogen intoxication the patient
spontaneously re-experiences some of the visual phenomena
that occurred during the intoxication (Abraham 1983;
Horowitz 1969).
Partial seizures may present with visual hallucinations:
in simple partial seizure the visual hallucination may constitute
the entire symptomatology of the seizure, whereas
in complex partial seizures, it will be accompanied by some
defect of consciousness.
Migraine headaches are typically preceded by an aura
consisting of a visual hallucination; these tend to be
simple, consisting of flashing lights or zigzagging lines
(Panayiotopoulos 1994; Russell and Olesen 1996). An aura
may, very rarely, persist long after the headache has
cleared, sometimes for years (Liu et al. 1995).
Blindness, whether partial or complete, may be associated
with either simple or complex visual hallucinations
in what is known as the Charles Bonnet syndrome
(Santhouse et al. 2000; White 1980). This syndrome has
been noted with visual loss caused by cataracts (Bartlett
1951), macular degeneration (Holroyd et al. 1992), and
lesions of the optic nerve, chiasm, tract and optic radiations
(Lepore 1990). Although classically the hallucinations
of the Charles Bonnet syndrome are said to be
‘Lilliputian’ in character, it in fact appears that such miniaturization
occurs in only a minority of patients with this
syndrome (Teunisse et al. 1994). The onset of the Charles
Bonnet syndrome can at times be quite dramatic: in one
case (White 1980), a 69-year-old man, while listening to
music, ‘suddenly saw a brightly coloured circus troupe
burst through the window’.
Focal intracerebral lesions, usually infarctions, may
cause hallucinations, and this has been noted with lesions of
the occipital lobe and adjacent temporal and parietal lobes,
and with lesions of the thalamus, mesencephalon or pons.
Lesions of the occipital cortex may, of course, also cause
a hemianopia, and in such cases the hallucinations tend to
occur in the hemianopic field (Kolmel 1985; Vaphiades
et al. 1996). The clinical presentation in such cases may be
quite remarkable: one patient (Lance 1976) with a left hemianopia
saw animals appearing: ‘from the left one at a time.
At various times he saw dogs, goats, a lion and a horse as well
as birds and butterflies. The animals would emerge from a
door on the left side of the room and walk to the mid-line. If
he looked to the left the animals retreated towards the door
but would advance again as he looked to the front’.
Another patient, a neurologist, after suffering an infarction
of the medial left occipital lobe, developed a right
hemianopia in which he experienced vivid visual hallucinations:
he noted that ‘often there was a pony with his head
cradled in my right arm’ (Cole 1999).
Hallucinations occurring secondary to mesencephalic
lesions are often referred to as ‘peduncular’ hallucinations,