Functional Abdominal Pain

Functional abdominal pain is chronic or recurrent abdominal pain not explained by an organic, structural or biochemical abnormality. It is not related to eating, bowel movements or menses to the degree needed for irritable bowel syndrome, functional dyspepsia or other defined functional disorders.

In adults, functional abdominal pain syndrome (also called centrally mediated abdominal pain syndrome) describes pain that is continuous or nearly continuous and present for at least 6 months. There is some loss of daily function. Physiological events (eating, defecation, menses) are unrelated or only occasionally related.

• It affects about 1 to 2% of adults. Women are affected more, with a peak in the fourth and fifth decades.
• It is the common cause of chronic abdominal pain in children. Functional abdominal pain disorders affect 10 to 20% of school age children, and the most common is irritable bowel syndrome or functional abdominal pain not otherwise specified.
• Mechanisms: dysregulation of the brain gut axis, with central amplification of normal visceral signals (central sensitisation), impaired descending inhibitory pain modulation, visceral hypersensitivity, and psychosocial factors (anxiety, depression, catastrophising, previous abuse or trauma, family illness behaviour, and stress). Previous gastroenteritis, abdominal surgery and chronic opioid use contribute.
• Associations: other functional disorders (irritable bowel syndrome, fibromyalgia, chronic pelvic pain, chronic fatigue, headache), psychiatric disorders (in up to 50 to 60%), and high health care use.
• Opioid use can produce narcotic bowel syndrome, a paradoxical worsening of abdominal pain with escalating opioid doses, and must be recognised.
• It is a diagnosis made after reasonable exclusion of organic disease. Positive features of the diagnosis (pain pattern, associated symptoms, normal examination, lack of alarm features, and psychosocial context) should be recognised, rather than relying on exclusion alone.

• Continuous or almost continuous abdominal pain (often described as dull, burning, gnawing, or cramping), poorly localised (often periumbilical or diffuse), unrelated to meals or bowel habits, and often disproportionate to examination findings. Pain disturbs daily activities, work and sleep.
• Associated features: other somatic symptoms (headache, back pain, fatigue, sleep disturbance), anxiety, depression, catastrophising, and a history of multiple negative investigations, many consultations or operations.
• Absent alarm features: no fever, weight loss, vomiting, bleeding, anaemia, nocturnal pain with waking, or abnormal examination.
• Examination: general health, normal weight, an anxious demeanour, a tender abdomen with a diffuse or inconsistent pattern, but no peritonism or mass, and no organomegaly. Abdominal wall tenderness test: pain that is unchanged or worse when the patient tenses the abdominal muscles (by lifting the head or legs) suggests an abdominal wall source rather than a visceral one.
• Differential diagnosis:
  • Other functional gastrointestinal disorders: irritable bowel syndrome, functional dyspepsia, and functional biliary or sphincter of Oddi disorders.
  • Abdominal wall pain: anterior cutaneous nerve entrapment syndrome, rectus sheath haematoma, hernia, myofascial pain, and thoracic spine referred pain.
  • Anterior cutaneous nerve entrapment syndrome causes a localised, sharp, positional pain that can be reproduced with palpation at a small tender point near the lateral border of the rectus muscle. It accounts for 10 to 30% of chronic abdominal pain.
  • Organic disease, gastrointestinal and gynaecological: coeliac disease, inflammatory bowel disease, chronic pancreatitis, peptic ulcer, gallstones, chronic mesenteric ischaemia, endometriosis, ovarian cysts, pelvic inflammatory disease, adhesions, chronic appendicitis, and Meckel diverticulum.
  • Organic disease, urological, vascular, metabolic and other: urological causes (kidney stones, chronic urinary tract infection), median arcuate ligament syndrome, superior mesenteric artery syndrome, hereditary angioedema, familial Mediterranean fever, acute intermittent porphyria, lead poisoning, diabetic ketoacidosis, Addison disease, hypercalcaemia, abdominal epilepsy, and abdominal migraine (in children).
  • Medicines and substances: opioids, NSAIDs, laxatives, and alcohol, and cannabinoid hyperemesis syndrome.
  • Eating disorders and somatic symptom disorder.
• Red flags:
  • Age above 50 years with new onset, unintentional weight loss, persistent vomiting, dysphagia, rectal bleeding or melaena, iron deficiency anaemia, nocturnal pain, fever, and jaundice.
  • An abdominal mass or localised tenderness, and progressive symptoms.
  • A family history of gastrointestinal cancer, inflammatory bowel disease or coeliac disease.
  • Abnormal blood tests (raised inflammatory markers, abnormal liver tests, raised calprotectin).
• Complications: disability, work absence, depression, anxiety, opioid dependence and narcotic bowel syndrome, unnecessary surgery (cholecystectomy, appendicectomy, hysterectomy, adhesiolysis), and nutritional compromise from restrictive diets.

• Clinical diagnosis, supported by a limited, targeted set of tests to exclude organic disease and to reassure the patient, avoiding repeated and invasive investigation.
• Take a full pain history (onset, character, location, radiation, severity, relation to meals, bowel movements, menses and position), associated symptoms, previous investigations and treatments, and medicines (including opioid and over-the-counter use).
• Also take the alcohol and drug history, the psychosocial history (stress, trauma, abuse, mood, work and family), and the impact on life. Identify the patient's own explanation and expectations.
• Baseline tests: full blood count, ferritin, C-reactive protein, urea and electrolytes, calcium, glucose, liver tests, amylase or lipase, thyroid function tests, coeliac serology (tissue transglutaminase IgA with total IgA), faecal calprotectin, urinalysis, and pregnancy test.
• Further tests depend on the picture:
  • Abdominal ultrasound or CT (gallstones, pancreatic disease, masses, adhesions).
  • Upper endoscopy or colonoscopy (alarm features or persistent dyspeptic or bowel symptoms).
  • Pelvic ultrasound or laparoscopy (gynaecological causes).
  • Doppler ultrasound or CT angiography (mesenteric ischaemia, median arcuate ligament syndrome in selected cases).
  • Porphyria screen (urine porphobilinogen during an attack), lead level, and abdominal wall tests.
  • Infiltration of a tender point with local anaesthetic (positive response supports abdominal wall pain).
• Screen for depression, anxiety and trauma, and assess opioid use.
• Avoid repeated imaging and invasive tests when the initial assessment is reassuring, as these reinforce illness belief.

• A positive diagnosis and a therapeutic relationship are the basis of treatment:
  • Acknowledge that the pain is real, explain the brain gut axis and central amplification of pain in simple terms, and avoid saying "nothing is wrong".
  • Set realistic goals (improved function and coping instead of complete cure), and arrange regular scheduled review rather than review only for flares.
  • Limit investigations, with a single clinician coordinating care.
• Non-drug therapy:
  • Cognitive behavioural therapy (8 to 12 sessions), gut directed hypnotherapy, mindfulness based stress reduction, and acceptance and commitment therapy, all of which improve pain and function.
  • Regular graded physical activity (30 minutes on most days), sleep hygiene, and stress management.
  • Dietary review to avoid unsupervised exclusion diets, with a dietitian when needed.
  • Heat application to the abdomen, and relaxation and breathing exercises.
• Neuromodulators (the first line drugs for centrally mediated pain), started at a low dose and titrated slowly, and given for at least 3 to 6 months:
  • Amitriptyline 10 mg orally at night, increased by 10 mg every 1 to 2 weeks to 30 to 75 mg at night (as tolerated), or nortriptyline 10 to 25 mg at night increased to 50 to 75 mg.
  • Review for dry mouth, constipation, drowsiness, and QT prolongation (obtain an electrocardiogram in older patients, in those with cardiac disease, or at doses above 50 mg).
  • Avoid tricyclics in glaucoma, urinary retention, recent myocardial infarction and with serotonergic drugs.
  • Duloxetine 30 mg orally once daily for 1 to 2 weeks, then 60 mg once daily (maximum 120 mg), with nausea, insomnia, and blood pressure rise as adverse effects. Avoid in severe hepatic and renal impairment, and with monoamine oxidase inhibitors.
  • Venlafaxine extended release 37.5 mg once daily, increased to 75 to 150 mg, as an alternative.
  • Citalopram 10 to 20 mg or sertraline 25 to 100 mg daily are used for comorbid anxiety or depression, with less evidence for pain.
  • Gabapentin 100 mg orally at night, increased every 3 to 7 days to 300 to 600 mg 3 times daily, or pregabalin 25 to 75 mg twice daily, increased to 150 mg twice daily (maximum 300 mg twice daily), for refractory pain.
  • Adverse effects of gabapentin and pregabalin include drowsiness, dizziness, weight gain and peripheral oedema. Reduce doses in renal impairment, and avoid abrupt cessation.
  • Quetiapine 25 to 50 mg at night, or low dose mirtazapine 15 mg at night, may be used as augmentation in specialist care.
• Opioids, benzodiazepines and long term NSAIDs:
  • Avoid opioids, benzodiazepines and long term NSAIDs.
  • If the patient is already taking opioids, arrange a gradual taper (reducing the daily dose by 10% every 1 to 4 weeks, or slower), with neuromodulators and psychological support, to treat narcotic bowel syndrome.
  • Use clonidine 0.05 to 0.1 mg orally 2 to 3 times daily for withdrawal symptoms during taper in specialist care. Refer to a pain or addiction service when needed.
• Antispasmodics and peppermint oil have a small benefit when intermittent colicky pain coexists: peppermint oil 0.2 mL enteric coated 3 times daily, hyoscine butylbromide 10 to 20 mg orally 3 to 4 times daily as needed, or mebeverine 135 mg 3 times daily before meals.
• Abdominal wall pain (anterior cutaneous nerve entrapment, myofascial pain):
  • Inject the tender point with lidocaine 1% 2 to 5 mL, with or without methylprednisolone 20 to 40 mg or triamcinolone 20 to 40 mg, giving relief in 60 to 80%.
  • A repeat injection after 4 to 6 weeks can be given. If there is a good response, nerve block or neurectomy is available in specialist centres.
  • Use lidocaine 5% patches 12 hours on and 12 hours off, or topical capsaicin 0.075% cream 3 to 4 times daily, for localised pain.
  • Physiotherapy for abdominal wall and core stretching.
• Children and adolescents (functional abdominal pain disorders):
  • Reassurance and explanation, regular school attendance, and family education to reduce attention to symptoms and avoid reinforcing sickness behaviour.
  • Cognitive behavioural therapy and hypnotherapy, a regular diet, and treatment of constipation.
  • Peppermint oil 0.2 mL enteric coated capsules 3 times daily (age over 8 years, weight above 45 kg, or 0.1 mL for 30 to 45 kg).
  • Avoid medicines unless pain remains severe. Then use low dose amitriptyline (0.25 to 0.5 mg/kg at night) or cyproheptadine 0.25 mg/kg per day in 2 divided doses (for abdominal migraine or functional pain in younger children, in specialist care).
  • Refer for red flags (weight loss, growth failure, blood, fever, vomiting, nocturnal symptoms, family history of inflammatory bowel disease).
• Special groups:
  • Pregnancy: use non-drug therapy, paracetamol, and cautious use of neuromodulators only when needed (avoid paroxetine, and review amitriptyline benefits and risks). Exclude obstetric and surgical causes.
  • Elderly: investigate more thoroughly for malignancy, mesenteric ischaemia and medicine effects, use lower neuromodulator doses, and avoid tricyclics in those with falls or cognitive impairment (prefer duloxetine with sodium monitoring).
  • Opioid users: a structured opioid taper reducing the daily dose by 10% every 1 to 4 weeks, with neuromodulators and specialist support.
  • Renal and hepatic impairment: reduce doses of gabapentin and pregabalin (renal), and avoid duloxetine in severe hepatic impairment.
  • Mental health comorbidity: integrate care, and treat depression, anxiety and trauma, with psychiatric referral when needed.
• Follow up: review every 2 to 4 weeks at first, reassess at 6 to 12 weeks, and then every 3 to 6 months once stable. Continue a drug for 6 to 12 months after good response before tapering. Refer to a gastroenterologist, pain medicine specialist or psychologist for refractory pain, diagnostic doubt, opioid dependence, or severe psychological distress.