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Written by Dr Lakshman Doddamani, James Paget University Hospital, Great Yarmouth, UK

“My friends at my school call me ‘Charlie Chatterbox’ because I can’t stop talking and am always getting into trouble with our teacher”, says Charlotte, “I was diagnosed with ADHD 2 years ago and I have been on medication ever since. I am so much better now than I used to be, but if I forget my tablets, I feel like my behaviour deteriorates, although I have learnt some tricks to help me control my impulsivity. I don’t know why I wasn’t diagnosed and put on these tablets earlier. I would have done much better in my school and might even have enjoyed it more.”

Is delayed diagnosis the price of being a girl with ADHD? We all know that ADHD is diagnosed three to four times more frequently in boys than in girls. The ratio of boys to girls with ADHD is up to 9:1 among children referred for clinical evaluation, whereas in community samples it is between 1:1 and 3:1.1 This discrepancy itself indicates that some girls with ADHD remain undiagnosed. Is the incidence of ADHD truly lower in girls than in boys, or is there another explanation for the difference in diagnosis rates? Do we understand the differences in the presenting symptoms of boys and girls, or are these being overlooked?

To help us answer these questions we need to go back to basics, looking at anatomical and functional differences between the brains of stereotypical boys and girls, and understanding how these might translate into pathological differences between the brains of boys and girls with ADHD. Any such pathological differences should then be cross-checked against the diagnostic criteria for ADHD, keeping in mind any social constraints that may also impact on the referrals received. It is also important to understand the action of sex hormones on the developing fetus, as this may be a key reason for anatomical differences in the brain structure of boys and girls, which could lead to functional differences.

Let’s look at the typical anatomical differences between the brains of boys and girls:

  • Male brains are approximately 10% larger2 and have greater lengths of myelinated axons3 than female brains.
  • Female brains have larger Wernicke’s and Broca’s areas, which are involved in processing language.4 Female brains also process verbal language in both sides of the front brain simultaneously, while male brains tend to process verbal language predominantly in the left side.5
  • Compared with male brains, the suprachiasmatic nucleus is elongated in female brains, with a greater surface area: this may influence circadian rhythms and their effects on hormones.6
  • The ratio of corpus callosum area to forebrain volume is greater in female brains than in male brains.7

These anatomical differences can lead to functional differences in the ways that boys and girls typically think. For example, girls are often thought to be more emotionally expressive and better able to interpret body language, whereas boys may attempt to control their feelings more.8

These differences are all secondary to the exposure of the unborn fetus to different ratios of sex hormones during the intrauterine period. It is also hypothesised that the hormonal effects of prenatal testosterone may make boys more vulnerable to the development of ADHD. Studies have suggested that high intrauterine concentrations of testosterone may be implicated in the aetiology of several neurodevelopmental disorders, including ADHD, autism and reading disability.9,10

It is important to note that diagnostic criteria for ADHD (eg the Diagnostic and Statistical Manual of Mental Disorders – fifth edition (DSM-5)11 have been primarily developed based on studies of predominantly male cohorts and have been suggested to focus largely on ‘externalising’ behaviours, more commonly observed in boys than girls.12 This means that current diagnostic criteria may have an inbuilt bias towards the diagnosis of ADHD as it manifests in males, and they may therefore not be as sensitive for the diagnosis of ADHD in females.

There are also differences in the types of ADHD that boys and girls typically present with. Girls tend to present with more inattentive behaviours than disruptive behaviours,12,13 which may mean that they are more difficult to identify with an untrained eye. This, I believe, is the most common reason why so many girls with ADHD remain undiagnosed until they present with comorbidities.

Some girls may present with a hyperactive type of ADHD, but it is important to remember that hyperactive girls may behave differently to hyperactive boys: girls tend to be hyper-talkative (like the girl described at the beginning of this article) and emotionally hyper-reactive, whereas boys are often unable to sit still.12

The perception of ADHD in society tends to be that ADHD only affects boys and that girls are ‘immune’ to the condition. As a result of this lack of understanding, girls with ADHD are often not brought to medical attention. Interestingly, in our recent, local, unpublished survey of teachers on the symptoms of ADHD in girls, very few identified talkativeness as one of the features suggestive of ADHD.

I would like to raise a very controversial point here, and ask whether we are discriminating against girls with ADHD by not bringing their symptoms to the attention of health professionals? My take on this is that we are not intentionally discriminating against them, but a lack of understanding of the differences in the presentation of ADHD between boys and girls may mean that girls are overlooked and are not referred to healthcare professionals as frequently as boys.

To conclude, the lower rates of diagnosis of ADHD in girls compared with boys is likely to be due to a combination of factors: a genuine lower incidence of ADHD in girls (due to hormonal effects) and a tendency for symptoms to remain unrecognised in girls, such that they may not be referred to health professionals appropriately. The only way to improve the recognition of ADHD in girls is through continued education of teachers, school nurses, GPs, mental health workers, psychiatric nurses and anyone else who comes into contact with children on a daily basis, on the recent advances in the diagnosis and management of both boys and girls with ADHD.14

 


Disclaimer: The views expressed here are the views of the physician and not those of Shire.

  1. Skounti M, Philalithis A, Galanakis E. Variations in prevalence of attention deficit hyperactivity disorder worldwide. Eur J Pediatr 2007; 166: 117-123.
  2. Durston S, Hulshoff HE, Casey BJ, et al. Anatomical MRI of the developing human brain: what have we learned? J Am Acad Child Adolesc Psychiatry 2001; 40: 1012-1020.
  3. Marner L, Nyengaard JR, Tang Y, et al. Marked loss of myelinated nerve fibers in the human brain with age. J Comp Neurol 2003; 462: 144-152.
  4. Harasty J, Double KL, Halliday GM, et al. Language-associated cortical regions are proportionally larger in the female brain. Arch Neurol 1997; 54: 171-176.
  5. Shaywitz BA, Shaywitz SE, Pugh KR, et al. Sex differences in the functional organization of the brain for language. Nature 1995; 373: 607-609.
  6. Swaab DF, Zhou J-N, Fodor M, et al. Sexual differentiation of the human brain. Biomedical Reviews 1997; 7: 17-32.
  7. Jancke L, Staiger JF, Schlaug G, et al. The relationship between corpus callosum size and forebrain volume. Cereb Cortex 1997; 7: 48-56.
  8. Niedenthal PM, Kruth-Gruber S, Ric F. Psychology and emotion (Principles of Social Psychology series). New York: Psychology Press, 2006.
  9. de Bruin EI, Verheij F, Wiegman T, et al. Differences in finger length ratio between males with autism, pervasive developmental disorder–not otherwise specified, ADHD, and anxiety disorders. Dev Med Child Neurol 2006; 48: 962-965.
  10. James WH. Further evidence that some male-based neurodevelopmental disorders are associated with high intrauterine testosterone concentrations Dev Med Child Neurol 2008; 50: 15-18.
  11. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Arlington, VA: American Psychiatric Press Inc, 2013.
  12. Quinn PO, Nadeau KG. Understanding girls with AD/HD – Part I: improving the identification of girls with AD/HD. Accessed 19 January 2017.
  13. Biederman J, Mick E, Faraone S, et al. Influence of gender on attention deficit hyperactivity disorder in children referred to a psychiatric clinic. Am J Psychiatry 2002; 159: 36-42.
  14. Anstel KM, Hargrave TM, Simonescu M, et al. Advances in understanding and treating ADHD. BMC Medicine 2011; 9: 72.
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