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The comorbidity of Fibromyalgia and ADHD

The interplay between Fibromyalgia (FM) and attention deficit hyperactivity disorder (ADHD) has been studied before, but relevance of the relationship is becoming more apparent. With ADHD diagnoses on the rise and the understanding of fibromyalgia broadening, it’s important to recognise the similarities in the symptoms and the underlying causes connecting these two conditions. In this blog, I discuss the overlapping relationship between FM and ADHD, explaining similarities in the presentation of symptoms and deeper into the dysfunctions in the brain and monoaminergic pathways.

Fibromyalgia (FM) is characterised by chronic muscle pain, tenderness, joint stiffness, chronic fatigue and sleep disturbances. The disorder is a lifelong condition that affects muscle and soft tissue, with the exact cause being unknown. Research suggests that the strengthening of synapses (long term potentiation) and changed activity of monoaminergic neuronal systems in the central pain pathway leads to heightened and long-lasting sensitivity to peripheral stimuli, causing physical manifestations. Certain factors can contribute to the development of the disorder, such as genetics, gender, physical or emotional trauma and infection.

Attention deficit hyperactivity disorder (ADHD) is a neurodivergent condition typically characterised by hyperactivity, impulsivity and attention deficit, of any combination. It has a strong genetic influence interplaying with environmental factors which can worsen the symptoms. The condition manifests itself as difficulties with executive functions such as organisation, planning, working memory and response inhibition, and nonexecutive functions including time perception, reaction time and memory storage. These disturbances can be seen as deficits in the prefrontal cortex and monoaminergic systems in the brain.

Symptoms

Firstly, the manifestation of symptoms in the two conditions are alike, one prevalent deficit is in cognitive functions. In Fibromyalgia (FM) patients, studies have shown that there are difficulties with slow reaction time, attention and inability to inhibit irrelevant information, all of which have been shown to be present in ADHD (Kofler et al 2020). Galvez-Sanchez et al (2018) reported that Fibromyalgia (FM) patients experienced forgetfulness, concentration difficulties and mental slowness. Using a series of neuropsychological tests, they revealed that Fibromyalgia (FM) patients had poorer performance in processing speed, attention, visuospatial and verbal memory, cognitive flexibility, mental planning and organizational skills. Similarly, in a study done by Mohammed et al (2021), results indicated dysfunction in reaction time for ADHD patients compared to healthy controls, as well as increased levels of distractibility. They also had impairments in selective attention and memory functions. Furthermore, the two conditions share similarities in pain sensitivity and perception. It is not unknown that Fibromyalgia (FM) patients experience sensitivities in pain, muscle weakness and reduced movement. This is evidenced in Staud et al’s (2021) study where they found not only a sensitivity to pain but also to innocuous stimuli like sound. Much like Fibromyalgia (FM), ADHD has been found to have higher and more widespread pain, which can be attributed to motor problems and higher muscle tone causing long term movement restriction (Stray et al 2013). Lastly, emotional dysregulation plays a massive part in both disorders, with the presence of alexithymia being apparent in both. This inability to recognise and regulate one’s internal emotional state explains a large proportion of Fibromyalgia (FM) psychosomatic symptoms such as anxiety and mood. Consequently, this exacerbates these symptoms and negatively affects mood, chronic sympathetic arousal and impairs immune status (Lumley et al 1996). In Soler-Gutiérrez et al’s systematic review (2023), they found emotional dysregulation to be a core symptom of ADHD. Alexithymia was also highly prevalent in ADHD adults (Edel et al 2010), with a large proportion expressing a greater intensity of emotions than controls and particular difficulty with accepting own emotions.

Neurobiology

When looking deeper at the causes of such symptoms, we can start to see the overlap between deficits in brain functions and neurotransmitter pathways that the two conditions experience. For Fibromyalgia (FM), the main defects lie in the monoaminergic neurotransmission system, which leads to an increase in glutamate and substance P and a decrease in serotonin and norepinephrine. Dopamine dysregulation is also observed, which all contribute to an imbalance in the brain and lead to the presentation of Fibromyalgia (FM) (Siracusa et al 2021). In an fMRI study done by Jensen et al (2009), participants were randomly presented subjectively calibrated pressure pain stimuli. They observed decreased connectivity in brain regions involved in pain inhibitory network such as the hippocampus, amygdala and brainstem in Fibromyalgia (FM) patients compared to healthy controls (HC). This implicates pain thresholds through functional and structural central sensitisation and reduces overall pain tolerance. The default mode network has also have been found to have reduced connectivity in Fibromyalgia (FM) during resting state, which has been linked to chronic pain symptoms and involved in affective aspects of pain perception (Chloe et al 2018), with chronic pain having an interruptive effect on attention. Likewise with ADHD, the monoaminergic neurotransmission system is dysregulated, particularly affecting dopaminergic and noradrenergic. Dopamine receptors are abundant in brain regions involved in reward circuits, learning memory and locomotor activity (da Silva et al 2023). Further, serotonergic and glutamatergic systems have also been implicated in ADHD from research suggesting altered levels of these neurotransmitters, much like Fibromyalgia (FM) (Wang et al 2018; Bauer et al 2018). Although the descending pain inhibitory network is not directly affected in ADHD, several brain processes that are interconnected, like the default mode network and motor networks, have been shown to have deficits in ADHD (Saad et al 2020), which have implications in pain perception and negatively affect attention, much like in FM.

Conclusion

As discussed, symptoms are highly comorbid between the two conditions, with the prevalence of ADHD being 44.72% in Fibromyalgia (FM) patients (Khalil et al 2018). This demonstrates the massive overlap in symptoms between the two conditions and highlights some interesting questions around the etiology and development of the disorders. Overall, we can see that the two conditions have very similar neurobiological underpinnings and share many of the same deficits in neurotransmitter systems. This is not to say that environmental factors do not play an important role in the development of the two conditions, which should be discussed in more detail, but brings to attention some important findings relating the two on a neurological level. This may help in developing better treatment options, assist with clinical diagnoses and may encourage healthcare professionals to look deeper into patients presenting with one of the conditions.

References

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