What is Functional Pain

Introduction

We often find ourselves calling the GP for symptoms such as tension headaches, abdominal pains or fatigue, which disrupt our daily activities. After numerous appointments and normal test results, we are given the label functional pain with a possible diagnosis of irritable bowel syndrome or fibromyalgia. The term functional pain can be confusing and frustrating, this article will clarify what this is, possible causes and treatment strategies.

Functional pain is:

• Pain without a clear cause such as a structural problem, inflammation or infection.¹
• Common examples are frequent abdominal pain, tension-type headaches or widespread aches with fatigue. 
• Very common with 15% of the population worldwide being affected.² 
• Costly with a large economic burden on the patient, their family and society. 

Functional pain syndromes are the name given to a set of symptoms with no clear cause affecting particular body systems. For example, a patient with functional abdominal pain may be given a diagnosis of irritable bowel syndrome (IBS), whereas a patient who has chronic fatigue and widespread aches and pain may be diagnosed with fibromyalgia. It is vital to understand functional pain as a staggering 15% of the population worldwide are affected.² Furthermore, it poses a large economic burden on the patient, their family and society. Functional pain syndromes are misunderstood and the exact cause is unknown. However, research has shown potential causes such as having a genetic predisposition, and psychological and environmental contributors.  

Types of pain

There are different types of pain such as the following:

• Nociceptive 
• Neuropathic 
• Functional

Nociceptive pain occurs when there is an injury to body tissue such as injuries to the skin, muscles, tendons, bones and joints. Nociceptive pain can be experienced as a sharp, achy or throbbing sensation. This pain can occur in the following situations: falling and scraping your knee, hitting your elbow, stubbing your toe or spraining your ankle. This pain may be acute but can also occur over a long period of time, known as chronic pain.³ 

Neuropathic pain occurs when there is damage to nerve tissue. Patients regularly complain of pain that is characteristically burning, shooting, stabbing, prickling, or a sensation of pins and needles.⁴ Examples of situations in which a person may experience this pain include the following: shingles, sciatica and pain that diabetic patients often experience in their hands and feet due to damage to small nerves, which is called diabetic neuropathy.⁴ Neuropathic pain may lead to someone being more sensitive to touch, hot and cold temperatures and movement. Patients may find it hard to feel changes in temperature.^3,4 A common experience of neuropathic pain is in the form of toothache when we eat something very cold. Our teeth may be damaged and the nerves inside may be exposed, causing this hypersensitivity. 

Functional pain can be defined as pain that occurs without a clear cause. This means there is no obvious infection, inflammation or structural problem that can be detected that could be the origin of the pain.¹ This pain occurs frequently and is bothersome and disruptive. Common sites in the body where a person may experience functional pain include the abdomen, the head, muscles, jaw, heart, and pelvis.²  A doctor will often conduct many tests to rule out diseases which could cause the pain. For instance, a person who has frequent abdominal pain may have tests to rule out conditions such as coeliac disease and inflammatory bowel disease. If tests show normal results and no obvious cause is found, they may be diagnosed with a condition such as irritable bowel syndrome or functional gastrointestinal disorders. Other diagnoses where a person experiences functional pain include: fibromyalgia, chronic fatigue syndrome/myalgic encephalomyelitis and tension-type headaches.⁵ These diagnoses are sometimes categorised under functional pain syndromes. 

Causes of functional pain

Whilst it is unclear what exactly causes functional pain, research has shown evidence that a genetic predisposition, environmental, and psychological factors are involved. A biopsychosocial model has been put forward and within this, each element can be seen to affect each other.⁵ 

Functional pain has been linked to psychological factors such as stress, anxiety and depression. Children with anxiety and depression are sometimes more vulnerable and at an increased risk of developing functional abdominal pain.⁶ Difficulties growing up such as adversity, trauma or bereavement may also make a child more likely to develop functional abdominal pain.¹  During periods of stress, patients may find their symptoms worsen. Furthermore, our perception of pain is influenced by our emotions and events that have occurred throughout our lives. A person who is experiencing anxiety and depression may pay more attention to the pain which can heighten the pain felt.⁷ Fibromyalgia, a functional pain syndrome in which a person experiences widespread aches, pains and fatigue, has been shown to be triggered by physical or emotional stress such as injuries, infections or stress.⁸ 

The table below summarises several theories that have been proposed to cause functional pain.⁵ These theories showcase different views on how pain perception can be altered.

Fibromyalgia has been shown to be caused by interactions between genetics and the environment. Polymorphisms, which are changes in the way a gene is expressed, in the catechol-O-methyltransferase (COMT) gene, the gene that helps to break down dopamine, adrenaline, and noradrenaline⁹, have been linked to fibromyalgia.² In addition to this, functional MRI scans of the brains of patients with fibromyalgia have shown an increased response to stimuli in the insula and anterior cingulate cortex.²  

In irritable bowel syndrome (IBS), nerve signals from the brain or stomach may make someone more sensitive to pain. The nerves between the gut and the brain may become oversensitive and certain normal sensations in the gut, that usually would be ignored, may be perceived as painful, known as visceral hypersensitivity.¹ These signals can be produced when the stomach or rectum is stretched, for instance, when food passes through the bowels.¹⁰ Sometimes the nerve receptors may become hypersensitive after repeated injury e.g. having numerous abdominal surgeries or infections, leading to even normal sensations in the abdomen being perceived as painful.⁷  

Read on section:

• Common conditions associated with functional pain e.g. fibromyalgia and IBS, and their treatments.

Fibromyalgia: 

Fibromyalgia is a common condition that is typically found in young women more than men. Patients with fibromyalgia experience symptoms such as persistent and chronic fatigue, widespread aches and pains and pain at light touch.¹¹ As mentioned earlier, psychological, genetics and environmental factors play a part in the development of this condition. 

Other factors, not yet mentioned, which can precipitate fibromyalgia include poor sleep, infections, autoimmune disorders and poor lifestyle. These patients also suffer from a psychological burden due to the condition. They may be subject to a lack of empathy and understanding from peers and doctors alike, further exacerbating their illness. Mental illness such as anxiety and depression have been associated with fibromyalgia. These may contribute to the development of the condition as well as be a byproduct of the condition.²

Treatment strategies for fibromyalgia target the biopsychosocial model and patient education is key to alleviate worries and address the psychological burden. Patients may be advised to carry out graded exercise, and yoga may help. Often antidepressants such as tricyclic antidepressants e.g. amitriptyline and SNRIs (selective serotonin and noradrenaline reuptake inhibitors e.g. duloxetine) may help alleviate pain.² CBT (cognitive behavioural therapy) may also help with patients perception of their pain and help increase their functional ability. Support groups such as Fibromyalgia Action UK are available. Other support groups can be found on - https://ukfibromyalgia.com/support-map. 

Irritable bowel syndrome (IBS):

Similar to fibromyalgia, IBS is more commonly found in young women and can often coexist with fibromyalgia. The prevalence rate of IBS is high in the population. Patients often experience abdominal pain, diarrhoea and/or constipation. The abdominal pain is often relieved after defecating. Treatment strategies may involve trialling antispasmodics such as Buscopan as well as CBT, relaxation, exercise and changes in diet e.g. eating homemade meals with fresh ingredients.¹² It may be helpful to see a dietician who can advise on certain diets that may help with symptom relief. The IBS Network, a national charity, provides information and advice about IBS. 

Summary 

To conclude, functional pain is pain without an obvious and clear cause such as inflammation, infection or structural abnormalities. Common conditions such as IBS and fibromyalgia are classed as functional pain syndromes. Whilst the cause of functional pain is not clearly known, a biopsychosocial model has been proposed. Several factors may contribute to the development of functional pain. These are: 

• Psychological problems such as stress, anxiety and depression, traumatic life events and early life adversity.
• Genetic predisposition: Having certain genes can predispose you to develop functional pain. The genetic and environmental interaction may lead to functional pain.

Therefore, treatment strategies often target this model. Treatments such as exercise, yoga, relaxation techniques, antidepressants and CBT have been shown to reduce functional pain. If you suspect you may have functional pain, it is important to discuss this with a doctor who will be able to conduct tests to rule out other causes and advise you on treatment. Support groups are available to help patients, such as Fibromyalgia Action UK and the IBS Network.