Chronic Pain in Autism (1):

The Invisible Burden

The study of pain sensation in autistic individuals has seen significant growth in research over the past few decades. Previous studies have primarily focused on pain sensitivity, indicating either a decreased sensitivity (hyposensitivity) or increased sensitivity (hypersensitivity) to pain in individuals with ASD.

Alley (2013) conducted a review of research papers to investigate the prevalent belief that autistic children and adults are insensitive to pain or have a high pain threshold. The review included five case studies that described individuals with ASD exhibiting pain insensitivity (Ross-Russell, Sloan 2005; Mieres et al. 2011; Bursch et al. 2004; Elwin et al. 2012; Rutherford 2005). However, the majority of the ten experimental studies reviewed indicated that the notion of pain insensitivity in ASD should be reconsidered (e.g., Nadar et al. 2004; Cascio et al. 2008; Daughters et al. 2007).

Previous observations have oversimplified the experience of pain in autism as insensitivity to painful stimuli. Findings in the past 15 years have challenged and complicated this dogma. While chronic pain is a frequent co-morbidity in autism, pain management in this population is often insufficient due to difficulties in pain evaluation, worsening their prognosis and perhaps driving higher mortality rates (Bogdanova et al. 2022).

Prevalence

Autistic children have an elevated prevalence of pain (15.65%) compared with children without ASD (8,2%). This disparity is more pronounced among children with ASD who have developmental comorbidities (19.9%). These findings may be due to several factors, including underlying sensory sensitivities, comorbid conditions associated with pain (e.g., cerebral palsy, genetic syndromes impacting gastrointestinal and other systems), and a higher frequency of medical procedures that can lead to short-term or long-term pain (Whitney & Shapiro 2019). 

Autistic patients are overrepresented in chronic pain clinics. The prevalence rate of autism may be closer to 30% in outpatient pediatric pain clinics. Over half (52%) of the autistic youth presented to the clinic with widespread pain, 60% identified as female, and 6% identified as gender expansive or transgender. Most of the autistic patients had co-occurring sensory-processing challenges, difficulty in describing their pain, emotions and somatic experiences, and exhibited cognitive inflexibility and social challenges (Han et al. 2024).

Causes

Pain is a complex neurobiological response with a multitude of causes. Autistic individuals often report experiencing chronic pain without a known cause. While numerous genes are implicated in ASD, only a few have been linked to varying degrees of pain comorbidity. Mutations in genes such as SCN9A, SHANK3, and CNTNAP2 have been shown to alter neuronal function, resulting in different pain responses in both mouse and human models (Brown et al. 2021).

However, relatively few studies investigate the physiological correlates of pain reactivity in ASD. Bogdanova et al. (2022) explore the possibility that atypical pain perception in people with ASD is mediated by alterations in pain perception, transmission, expression and modulation, and through interactions between these processes. These complex interactions may account for the great variability and sometimes contradictory findings from the studies. The researchers propose a model of the pain cycle that includes the interplay between the molecular and neurophysiological pathways of pain processing and conscious appraisal, which may interfere with pain reactivity and coping in autism, as well as the social factors in pain-induced response.

Sensory processing issues can amplify the experience of pain in autistic individuals. Hoffman et al. (2023) tested excitatory-inhibitory imbalance (a mechanism underlying autism) for pain processing. The results showed that autism is associated with a pronociceptive pain modulation profile expressed by hypersensitivity to daily stimuli and experimental pain and less-efficient inhibition of tonic pain. Hypersensitivity to experimental pain was attributed to greater autism severity and sensory hypersensitivity to daily stimuli.  

In a separate study, Jordan et al. (2024) focused on chronic pain experiences in autistic adolescents, identifying two key themes: (1) “overstimulated and striving for control" describing how heightened sensitivity enhanced adolescents' levels of anxiety and subsequent pain, illustrating a reciprocal relationship between anxiety, pain, and sensory element; and (2) "not everyone fits the mold" capturing how autistic adolescents positioned themselves as distinct from others due to the unique nature of being autistic and living with pain. This sense of difference negatively impacted their ability to engage with and benefit from the standard treatment for chronic pain.

Dubois et al. (2020) examined endogenous pain modulation mechanisms in autistic adults without intellectual disabilities. Statistical analyses indicated that endogenous pain modulation mechanisms in ASD group did not differ significantly from those of healthy adults. The pain scores were very disparate in ASD group with a greater range of extreme scores than in control group. Unlike schizophrenic patients, there was no systematic dysfunction of endogenous excitatory pain modulation mechanisms, but the high variability necessitates caution in interpreting the results and formulating conclusions.

Comorbidities

Autistic individuals may have co-occurring conditions that can contribute to the experience of chronic pain. ASDs and joint hypermobility-related disorders are broad terms used to describe two distinct groups of pathologies that typically manifest in childhood. These conditions are studied by various medical specialties, with psychiatry focusing on ASD and musculoskeletal disciplines and genetics addressing hypermobility-related disorders. Despite limited research, there is a growing body of evidence suggesting a potential link between these conditions, indicating a higher likelihood of co-occurrence than previously believed.

Hypermobility is often a characteristic of hereditary connective tissue disorders, such as Ehlers-Danlos syndromes and Marfan syndrome, which are known for their multisystem fragility leading to issues with proprioception, motor coordination, and increased susceptibility to trauma and chronic pain. Individuals with ASD may be at risk for untreated chronic pain due to challenges in communication and diagnosis, making it crucial to raise awareness about the potential connection between ASD and hypermobility-related disorders. By recognising this link, healthcare professionals can better identify ASD patients who may be predisposed to chronic pain and provide appropriate care and support (Baeza-Velasco et al. 2018).

Gastrointestinal issues, such as irritable bowel syndrome, are common in individuals with ASDs and can cause significant pain and discomfort. Autistic females are more likely than their male counterparts with ASD to suffer from GI-related disturbances and chronic pain (Davies et al. 2023).

Sleep disturbances, anxiety, and depression are also common in individuals with autism and can exacerbate existing pain conditions. These comorbidities can further complicate the diagnosis and management of chronic pain in individuals with autism.

Understanding and addressing chronic pain in autistic individuals requires a multifaceted approach that considers sensory processing issues, genetic factors, and co-occurring conditions. The complexity and variability of pain experiences in autism challenge oversimplified notions of pain insensitivity and highlight the need for tailored pain management strategies.