Chronic pain syndromes

Chronic pain may occur after some acute injuries, as part of degenerative diseases, or as a result of a primary condition (e.g., migraine and fibromyalgia). The causes of chronic pain are many and can be considered to be due to musculoskeletal (mechanical) causes, neurological causes, causes of headache, psychological causes or localised disease, or as part of a generalised disease process.

Musculoskeletal (mechanical) causes:

• Myofascial pain

• Osteoarthritis

• Rheumatoid arthritis

• Osteomyelitis

• Osteoporosis

• Ankylosing spondylitis

• Fractures

• Chronic or repetitive overuse

• Muscular strains

• Faulty posture

• Mechanical low back pain

• Polymyalgia rheumatica

• Polymyositis.

Neurological causes:

• Postherpetic neuralgia: pain persisting for more than 1 month after the onset of herpes zoster (occurs in about 30% of patients following acute zoster, and lasts 1 year in about 10%)[19]Scott FT, Leedham-Green ME, Barrett-Muir WY, et al. A study of shingles and the development of postherpetic neuralgia in East London. J Med Virol. 2003;70 Suppl 1:S24-30. http://www.ncbi.nlm.nih.gov/pubmed/12627483?tool=bestpractice.com

• Complex regional pain syndrome: develops following an identified injury or period of limb immobilisation (e.g., casting) and may be divided into type 1 (occurring in the absence of a nerve injury; formerly called reflex sympathetic dystrophy) and type 2 (occurring after injury to a specific large nerve; formerly called causalgia)

• Diabetic sensorimotor polyneuropathy (up to 25% of people with diabetes)

• Spinal stenosis

• Brachial plexus traction injury

• Thoracic outlet syndrome

• Trigeminal neuralgia

• Alcoholism

• Thyroid disease

• Pernicious anaemia

• Infections (e.g., HIV)

• Polyneuropathies

• Polyradiculopathies.

Causes of headache:

• Migraine

• Trigeminal neuralgia

• Giant cell (temporal) arteritis

• Glaucoma

• Smoking

• Alcohol

• Temporomandibular joint dysfunction

• Medication overuse.

Psychological causes:

• Depression

• Anxiety

• Personality disorders

• Sleep disturbances.

Localised or regional pain may involve specific sites or regions:

• Abdominal (peptic ulcer, irritable bowel syndrome, pancreatitis, hernias, diverticular disease, etc.)

• Female reproductive system (pregnancy, endometriosis, chronic salpingitis, etc.)

• Male reproductive system (prostatitis, testicular torsion, etc.)

• Urological (urolithiasis, interstitial cystitis, etc.)

• Cardiovascular (angina, peripheral vascular disease, etc.).

Widespread pain may occur in conjunction with a wide variety of systemic illnesses:

• Rheumatological conditions:

  • Ankylosing spondylitis

  • Fibromyalgia

  • Osteoarthritis

  • Osteomalacia

  • Polymyalgia rheumatica

  • Rheumatoid arthritis

  • Sjogren syndrome

  • Systemic lupus erythematosus (SLE).

• Endocrinological conditions:

  • Diabetes

  • Hyperparathyroidism

  • Hypothyroidism.

• Infectious diseases:

  • Chronic hepatitis C

  • HIV infection

  • Lyme disease.

• Cancer:

  • Metastatic cancer

  • Multiple myeloma

  • Paraneoplastic syndrome

  • The effects of radiation, chemotherapy, or surgical treatment of cancer.

Two types of peripheral pain fibres transmit to the spinal cord (A-delta fibres and C fibres). Two pathways transmit from the spinal cord to the supraspinal areas: (1) the sensory pathway from lamina V in the dorsal horn of the spinal cord to the hypothalamus and somatosensory cortex; and (2) the affective pathway from lamina I in the dorsal horn of the spinal cord to the hypothalamus, amygdala and cingulate area. Pain can be modulated at the level of the periphery or spinal cord, or from higher supraspinal areas.

In general, chronic pain is believed to occur in response to changes in sensitisation in peripheral and central pain pathways, along with alterations in a variety of important neurotransmitters, including serotonin, noradrenaline, and dopamine.[20]Jeong Y, Holden JE. Commonly used preclinical models of pain. West J Nurs Res. 2008 Apr;30(3):350-64. http://www.ncbi.nlm.nih.gov/pubmed/18029542?tool=bestpractice.com

International Classification of Diseases 11th revision (ICD-11): chronic pain[1]World Health Organization. ICD-11 for mortality and morbidity statistics. 2022 [internet publication]. https://icd.who.int/browse11/l-m/en

Chronic pain is pain that persists or recurs for longer than 3 months. Chronic pain is multifactorial: biological, psychological, and social factors contribute to the pain syndrome.

Chronic primary pain: chronic pain in one or more anatomical regions that is characterised by significant emotional distress (anxiety, anger/frustration, or depressed mood) or functional disability (interference in daily life activities and reduced participation in social roles).

Chronic cancer-related pain: pain caused by the primary cancer itself or metastases (chronic cancer pain) or its treatment (chronic post-cancer treatment pain).

Chronic post-surgical or post-traumatic pain: pain developing or increasing in intensity after a surgical procedure or a tissue injury (involving any trauma including burns) and persisting beyond the healing process (i.e., at least 3 months after surgery or tissue trauma).

Chronic secondary musculoskeletal pain: pain arising from bone(s), joint(s), muscle(s), vertebral column, tendon(s), or related soft tissue(s).

Chronic secondary visceral pain: persistent or recurrent pain originating from internal organs of the head/neck region and of the thoracic, abdominal, and pelvic cavities.

Chronic neuropathic pain: pain caused by a lesion or disease of the somatosensory nervous system.

Chronic secondary headache or orofacial pain: comprises all headache and orofacial pain disorders that have underlying causes and occur on at least 50% of the days during at least 3 months. The duration of pain per day is at least 2 hours.

Other specified chronic pain: used if a pain condition persists or recurs for longer than 3 months.

Chronic pain, unspecified: used if a pain condition persists or recurs for longer than 3 months.

Practical clinical categorisation of chronic pain syndromes, based on major pain features

Chronic pain may be localised (regional) or generalised and is typically divided into 5 main possible categories, based on symptoms and presumed aetiology.

• Myofascial (skeletal muscle and fascia/connective tissue surrounding muscle) pain:

  • • Lateral epicondylitis (tennis elbow)

    • Quadratus lumborum syndrome (a common cause of non-radicular low back pain)

    • Piriformis syndrome (a cause of buttock and hip pain).

• Musculoskeletal (mechanical) pain:

  • • Osteoarthritis

    • Rheumatoid arthritis

    • Back pain.

• Neuropathic pain:

  • • Peripheral neuropathy

    • Postherpetic neuralgia (shingles)

    • Complex regional pain syndrome

    • Central pain - post-stroke pain and multiple sclerosis pain.

• Fibromyalgia:

  • • Chronic, widespread pain with multiple trigger points.

• Chronic headache:[2]Headache Classification Committee of the International Headache Society (IHS). The international classification of headache disorders, 3rd edition. Cephalalgia. 2018 Jan;38(1):1-211. https://journals.sagepub.com/doi/10.1177/0333102417738202 http://www.ncbi.nlm.nih.gov/pubmed/29368949?tool=bestpractice.com

  • • Cluster (idiopathic; intermittent; strictly unilateral; orbital, supraorbital, temporal, or in any combination of these sites; lasting 15 to 180 minutes; occurring from once every other day to eight times a day)

    • Tension-type (primary headache; typically bilateral; constant [non-pulsating]; lasting minutes to days; defined as episodic [1-14 days/month on average] or chronic [≥15 days/month on average for >3 months])

    • Persistent headache attributed to traumatic injury to the head or neck (post-traumatic-headache; reported to have developed within 7 days of injury that persists for more than 3 months after onset)

    • Chronic migraine (primary headache; unilateral or bilateral; pulsating; lasting up to 72 hours; with or without aura)

    • Drug overuse (headache occurring on ≥15 days per month on a background of a pre-existing primary headache disorder and developing as a consequence of regular overuse of acute or symptomatic headache drug for more than 3 months).