Obsessive-compulsive Disorder 133However, it is important to remember that children and adolescents
with autistic spectrum disorders do sometimes develop an additional
OCD that may respond well to behavioural therapy or medication.
5 Schizophreniacan be accompanied by obsessions and compulsions. It
is important to clarify if an ‘obsession’ is actually a voice, and if a
‘compulsion’ is actually a response to a command.
6 Anorexia nervosahas obsessive-compulsive qualities relating to food and
exercise, but these do not automatically warrant an additional OCD
diagnosis. Conversely, OCD may involve avoidance of ‘contaminated’
food, or compulsive exercising, but this does not warrant a comorbid
diagnosis of anorexia nervosa if the child or adolescent has a realistic
body image. In some instances, though, OCD and eating disorders do
genuinely co-exist.
7 Tourette syndromeis commonly accompanied by obsessive-compulsive
features, sometimes amounting to OCD (see Chapter 15). Complex tics
preceded by an ‘urge’ are arguably compulsions by a different name.
Since family studies suggest that the same genes may increase liability
to both tics and OCD, it is less surprising that the phenomenology of tics
and OCD also overlaps.
Causation
The disorder often emerges insidiously without any evident precipitant.
Even when parents or young people can identify a precipitant, the re-
sponse is generally disproportionate to the initiating stress. It is likely that
constitutional vulnerability is important in many cases. Despite an earlier
enthusiasm for psychodynamic explanations, current theories emphasise
biological and behavioural explanations. Judging from neurological and
neuroimaging studies, OCD involves structural or functional abnormalities
affecting the basal ganglia, frontal lobe regions (orbitofrontal and anterior
cingulate) and thalamus. From an ethological perspective, compulsions
can perhaps be seen as fixed action patterns related to grooming and
cleaning that have escaped suppression by ‘higher centres’ and taken on
a life of their own. Once initiated, rituals may persist because of their
anxiety-reducing effects.
A positive family history of OCD is fairly common, and twin studies sug-
gest a heritability of around 50%. Several studies support the involvement
of a candidate gene (SLC1A1) involved in glutamatergic neurotransmis-
sion (which plays a part in cortico-striate connections). Tic disorders and
OCD may cluster in the same families, suggesting that these disorders may
sometimes reflect the same underlying gene or genes (see Chapter 15).
There may be other genes that predispose to OCD but not to tic disorders.
In some instances, OCD has a sudden onset accompanied by other acute
symptoms such as tics, emotional lability, disruptive behaviour, atten-
tional difficulties, depression, and sleep disturbance. These are sometimes
referred to as childhood acute neuropsychiatric symptoms (CANS) and