dual diagnosis: autism and other medical conditions

Many theories have been advanced for the causes of autism. Before looking at them in more detail, I want to examine a broader issue; the association between known medical disorders and autistic characteristics.

In their book The biology of the autistic syndromes, Christopher Gillberg and Mary Coleman devote an entire section (six chapters) to medical conditions associated with a formal diagnosis of autism. (My copy is of the 2nd edition published in 1992; the 1st edition came out in 1985, the 3rd in 2000 and the 4th, entitled The Autisms was published in 2012.) The authors don’t speculate on how the medical conditions they list might be related to autism, but it’s clear from this and later works that they are of the view that there are ‘autisms’, rather than a single disorder with different manifestations. From the preface of The Autisms;

Although Kanner, who first accurately described autism in 1943, likely assumed it was a single disease entity…over time it became clear that this was not so, as multiple studies… were published. Instead autism was found to be a specific set of symptoms found in a conglomeration of different diseases some of which overlapped with the intellectual disability/mental retardation syndromes.” (p.xi)

I think Gillberg and Coleman are suggesting that autistic characteristics (which by definition form a syndrome) arise as a consequence of a range of medical conditions, implying that the causes for autistic characteristics are probably different in different patients – hence the authors referring to ‘autisms’ in the plural. In 1974 Coleman had studied a group of 78 autistic children. In an interview with Adam Feinstein for A History of Autism, she says;

As a result of this [1974] study, I came to realize that autism is like mental retardation – it’s a final common pathway in the brain affected by many different underlying causes, many different disease entities.” (p.147)

I’ve summarised below the ‘disease entities’ listed by Gillberg and Coleman as associated with autism. (The list is from the 1992 edition; later research has expanded on it.)

Gillberg & Coleman's disease entities associated with autism

Gillberg and Coleman are by no means the only authors to identify an association between autistic characteristics and other medical disorders. Here are the ‘organic conditions’ reported by Wing and Gould (1979) in children who met Kanner’s criteria in their Camberwell study:

maternal rubella
infantile spasms
severe perinatal complications
multiple congenital abnormalities
unconfirmed viral illness under 1 year
gastroenteritis under 1 year
unconfirmed head injury under 1 year
operation for cleft palate under 1 year.

Michael Rutter and Eric Schopler (1988) comment:

The last issue concerns the question of etiological heterogeneity within the field of autism syndromes. We have already noted that there is undoubted heterogeneity. The very fact that the clinical picture of autism can arise from diseases as diverse as congenital rubella, tuberous sclerosis, encephalopathy, infantile spasms with hypsarrhythmia, cerebral lipoidosis and neurofibromatosis makes that clear.” [references omitted](p.28)

Patterns of association

Because autistic characteristics involve high-level processes, the relationships between autistic disorder and other medical disorders are likely to be complex and varied. However, the relationships between autistic characteristics, somatic symptoms and underlying causes will fall into one of four basic patterns, as shown below.

relationship between autistic characteristics, somatic symptoms and underlying causes

The section on other medical conditions in Gillberg and Coleman’s book was originally entitled “Disease entities that have a subgroup of patients with autistic symptoms” – in other words, not all children diagnosed with a particular disease entity were autistic, suggesting that for each disease entity:


the sub-group of children with autistic symptoms had a distinct second disorder (an autistic syndrome)


the sub-group of children with autistic symptoms had a predisposition to develop those symptoms and that they have been triggered by the disease entity.

Patterns of association and diagnosis

Depending on how strong the association is between autistic characteristics and a particular medical disorder, diagnosis is likely to proceed as follows;

A. If a medical disorder (e.g. disorder A) is frequently associated with autistic symptoms, it’s likely that the medical disorder will be assumed to account for the autistic symptoms and the child will get a single diagnosis of disorder A.

B. If a medical disorder (e.g. disorder B) is only occasionally associated with autistic symptoms, it’s likely that the medical disorder will be assumed not to account for the autistic symptoms and the child will get a dual diagnosis of disorder B and autistic disorder.

C. If the child has somatic symptoms that don’t fit the criteria for any known medical disorder, unless severe, those symptoms are likely to be overlooked and the child will get a diagnosis relating only to their behaviour – autistic disorder.

Each of these options is problematic if the cause of the child’s symptoms is to be identified, because in each group – A, B or C – the autistic characteristics might or might not be caused by whatever causes the somatic symptoms. The only ways to find out would be either to investigate all the symptoms shown by each individual, or to look at the differences between individuals who are autistic and those who aren’t, in respect of each of the other medical disorders.

What isn’t helpful is to assume that everybody’s autism has the same cause.

Coleman, M & Gillberg, C. (2012) The Autisms (4th edn). Oxford University Press.
Feinstein, A. (2010). A History of Autism. Wiley-Blackwell.
Gillberg, C. & Coleman, M. (1992) The Biology of the Autistic Syndromes (2nd edition). Mac Keith Press.
Rutter, M. & Schopler, E. (1988). Concepts and diagnostic issues in E. Schopler & G.B. Mesibov (eds.) Diagnosis and assessment in autism. Springer.
Wing, L. & Gould, J. (1979). Severe impairments of social interaction and associated abnormalities in children: Epidemiology and classification, Journal of Autism and Childhood Schizophrenia, 9, 11-29.


autism: syndrome under suspicion

This is the last post about syndromes. Promise. The reason I keep referring to syndromes is this: In recent years ‘autism’ as a label for a set of symptoms has become confused with ‘autism’ as a label for an underlying medical condition assumed to cause those symptoms. This confusion, in my view, has placed a major obstacle in the path of autism research. In this post, I round up what we know about syndromes, imagine being a doctor in the heyday of syndromes a century ago, and then expand on the two different uses of the word ‘autism’.

What we know about syndromes

Emil Kraepelin classified mental disorders in terms of syndromes. This approach makes perfect sense because:

1. A syndrome consists of signs and symptoms that tend to co-occur. (Technically, a sign is something someone else can detect, and a symptom is what the patient reports, but for the sake of brevity, I’ll refer to both as symptoms).

2. Symptoms that tend to co-occur are more likely to be causally linked than symptoms that don’t, so identifying a syndrome can provide an important clue as to what’s causing the symptoms.


3. The fact that symptoms tend to co-occur doesn’t guarantee that they are causally linked. Correlation doesn’t indicate causality.

4. The symptoms could all share the same cause; some symptoms could be causally linked, but not others; the causal links could be complex; or the symptoms could co-occur by chance.

Dr Smith’s syndrome

To illustrate the advantages and disadvantages of classifying symptoms in terms of syndromes, I’m going to imagine a doctor – Dr Smith – who has a successful medical practice in a large country town and tries to keep up to date with advances in medicine. It’s 1912. During the last month, Dr Smith has seen over a hundred patients with the same symptoms; breathing difficulties, a persistent cough and chest pain. His experience tells him that the sudden onset of such symptoms in a large number of patients living in the same geographical area indicates that the cause is likely to be a contagious disease. The course of the illness in the first few cases allows Dr Smith to reassure his patients that if they rest, keep warm and take plenty of nourishing broth they will probably be as right as rain within a week or two.

Like any diligent doctor, Dr Smith keeps notes on his patients’ progress. After the first half-dozen cases, he stops listing all the symptoms and writes ‘respiratory disorder’ as shorthand for breathing difficulties, cough and chest pain. If patients have other symptoms besides the three main ones, he makes a note of that. If patients don’t have all the core symptoms, he notes that too. The core symptoms Dr Smith has observed are so common that he wouldn’t dream of claiming that he’d found a new syndrome, but his ‘respiratory disorder’ is a syndrome nonetheless, and he would refer to it as such. It consists of core symptoms that tend to co-occur, but the severity of the symptoms varies between patients and some patients have additional symptoms.

Dr Smith is aware that although most patients with the syndrome ‘respiratory disorder’ will recover quickly because their symptoms are caused by a mild infection, the core symptoms of ‘respiratory disorder’ can also be caused by more serious illnesses such as pneumonia, tuberculosis or an allergic reaction to dust, so he keeps a careful eye on how his patients’ symptoms change. His patients have every confidence in him – but what does Dr Smith’s syndrome have to do with autism?

Autism as a descriptive term

The syndrome labelled ‘autistic disorder’ in DSM-IV has three core symptoms – impairments in social interaction and communication, together with restricted, repetitive behaviours. As far as the process of diagnosis is concerned, ‘autistic disorder’ is an exact parallel to Dr Smith’s ‘respiratory disorder’ – except of course that the causes, core symptoms and outcomes are different. Dr Smith used the term ‘respiratory disorder’ to describe the core symptoms of a syndrome, but he knew that there could be several causes for those symptoms. For many years, ‘autism’ and ‘autistic’ were also used descriptively. Bleuler, Kanner, Asperger, Eisenberg, Wing, Gould and a host of other medical practitioners between 1911 and 1979 used ‘autism’ to describe symptoms. DSM-IV also uses ‘autistic’ descriptively; autistic disorder is a disorder characterised by autistic features, ‘autistic’ being an adjective that describes behaviour, just as ‘excitable’ or ‘lethargic’ do.

Autism as a medical condition

Since 1979, a different use of the word ‘autism’ has crept into general use, and even into specialized use. It’s now used to refer to an underlying medical condition that is assumed to cause autistic behaviour. Why does that matter? It matters because what has also crept in is the assumption that if people meet the diagnostic criteria for autistic disorder, that means they have the underlying medical condition that causes autistic behaviiour – that everybody’s autistic characteristics must have the same cause.

That assumption is of crucial importance, because even if you find a genuine syndrome – a group of symptoms that do reliably co-occur – it doesn’t follow that all those symptoms are causally related, something that our fictitious Dr Smith was well aware of. Kanner was aware of it too; he refers to his syndrome as ‘unique’. This wasn’t any old group of symptoms that happened to crop up in eleven children but overlapped here and there in other children; his syndrome consisted of twenty (count ’em) essential common characteristics – how likely was that to happen by chance? Furthermore, Kanner also thought he’d found the cause of all those symptoms; what tied them together was a disturbance of affective contact. That explained everything, including the children’s abnormalities in feeding, speech and motor movement. But Kanner’s causal link between symptoms – a disruption of the social instinct – was based on an assumption made by psychodynamic theory. Not only does later research suggest that there’s little evidence for the existence of a social instinct, it also shows that Kanner was wrong about the symptoms he observed making up a syndrome.

As the number of children diagnosed with his syndrome increased, Kanner found he had to omit some of the symptoms because many children didn’t show them. He also had to group the remaining symptoms under five headings, because not all the children showed all the ones that were left. What Wing and Gould found in their epidemiological study was that although some children did meet the criteria for Kanner’s syndrome, there were no clear-cut differences between them and the rest of the socially impaired group. Wing and Gould pointed out that although social impairment was reliably associated with two other symptoms – i.e. it was part of a syndrome – that syndrome wasn’t clearly differentiable from social impairments in general. Indeed its symptoms formed a spectrum because they varied considerably in severity and blurred into each other.

Despite what Wing and Gould’s conclusions, a common current perception of autism is not that it’s a descriptive term for a rather vague group of symptoms that might have lots of different causes, but that it is a single medical condition that manifests itself in different ways in different individuals. The DSM and ICD, although technically using the word ‘autistic’ or ‘autism’ descriptively (the ICD equivalent of ‘autistic disorder’ is ‘childhood autism’), reinforce that idea in respect of autism and many other so-called mental disorders. That’s because they are both arranged in the form of labels for syndromes followed by a list of their symptoms, giving the impression that we know that these disorders exist, and we know what their symptoms are. All that remains is to find those elusive and complex causes.

Diagnostic criteria: the effect on research

This way of thinking about autistic characteristics in particular and mental disorders in general, poses a major problem for researchers. Many researchers are aware that we don’t actually know that the symptoms labeled ‘autistic disorder’ in the DSM (‘childhood autism’ in the ICD) are causally linked, and there might be different causes for the same symptoms in different cases, but the only way researchers can locate autistic research participants is by using the diagnostic criteria set out in the DSM or ICD. In many cases, for research purposes autistic participants are required to be diagnosed using specific standardized assessments. This process might look as if it ensures that all the autistic participants form a homogeneous group. They meet the same diagnostic criteria, certainly, but if those diagnostic criteria by definition put people with similar symptoms but different causes for those symptoms into the same basket, the researchers are in effect trying to find differences between a group of apples-and-oranges and a group of pears. Or more accurately, a group of apples-and-oranges and a group of mixed fruit. There will be some differences between the groups, but they are unlikely to shed any light on what causes apples to develop as apples, or what causes oranges to develop as oranges.

One by one, theories about the causes of autistic characteristics have been sidelined because none of them has explained the characteristics of everyone who meets the diagnostic criteria for autism. Studies investigating ‘refrigerator mothers’, sensory processing, theory of mind, executive function, central cognitive coherence, the extreme male brain, vaccines and dietary intolerances have all produced interesting and useful findings, but have all fallen by the wayside because those findings have also tended to be inconclusive and contradictory – not for the specific individuals involved but for people with autism in general. If everyone diagnosed with autistic disorder showed identical symptoms and we knew that all those people had the same cause for their symptoms, inconclusive and contradictory findings would indeed be frustrating and puzzling. But since autistic characteristics vary widely and we don’t know that all autistic people have the same causes for their symptoms, the most likely explanation for inconclusive and contradictory research findings is that there are several different causes for autistic characteristics (different causes in different people), but the diagnostic criteria lump them together regardless.

In the next post, I want to explore why that happens.

Illustration: this work by Phillip Martin is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.