Primary and Secondary Chronic Pain Classifications

Chronic pain is now considered a disease all on its own due to the impact it has, and the World Health Organization (WHO) has advanced recognition and treatment of chronic pain with two classifications: chronic primary pain and chronic secondary pain. Both classifications are divided into multiple subgroups, all of which can help your healthcare provider diagnose and treat your chronic pain.

Why Pain Is a Disease

It might seem odd to think of pain as a disease, and the concept has been controversial in the medical community. However, chronic pain is one of the most frequent reasons people go to the healthcare provider and is a major cause of disability and suffering. Because it’s not life-threatening, people may live with it for decades, which means its personal and the societal burden is massive. People with chronic pain are more likely to be unemployed, face difficulty with daily activities, and have poorer overall health.

Despite its impact, chronic pain has only recently had a place in the International Classification of Diseases (ICD), which is a tool for gathering data on death and disease around the world. In 2018, with the eleventh edition (ICD-11), the WHO included it and established official criteria for both primary and secondary chronic pain. 

Those classifications allow for more consistent recognition and diagnosis of chronic pain conditions and help establish treatment goals and paths for the millions of people living with chronic pain. 

What Do Primary and Secondary Mean?

In medicine, “primary” is used to describe a condition that’s not caused by a different medical condition, while “secondary” means it is a consequence of another condition. For example, someone with secondary insomnia may have trouble falling asleep because of pain, stress, or acid reflux that occurs when they lie down. Someone with primary insomnia simply has difficulty falling asleep and it's not caused by another medical condition.

Chronic Primary Pain

The ICD-11 defines chronic primary pain as pain that:

• Is in one or more region of the body
• Persists for longer than three months
• Is associated with significant emotional distress or functional disability
• Cannot be explained by another chronic condition

This includes pain syndromes that are generally thought of as conditions in their own right. Subtypes of chronic primary pain all have to meet those criteria. The ICD-11 subtypes include: 

• Widespread pain
• Complex regional pain syndrome 
• Chronic primary headache and orofacial (mouth and face) pain
• Chronic primary visceral (internal organ) pain
• Chronic primary musculoskeletal pain
• Other specified chronic primary pain
• Unspecified chronic primary pain

Widespread Pain

Chronic widespread pain (CWP) is defined as diffuse pain in at least four out of five regions of the body. Fibromyalgia is the main diagnosis under this category.

Fibromyalgia is believed to be a condition of central sensitization, which is a hypersensitive central nervous system that converts some normal sensations to pain (allodynia) and heightens the sensation of pain (hyperalgesia).

Other symptoms of fibromyalgia include:

• Fatigue
• Nonrefreshing sleep
• Cognitive dysfunction (“fibro fog”)
• Dizziness
• Sensitivity to heat and cold
• Sensitivity to light, noise, or fragrances

Complex Regional Pain Syndrome

Complex regional pain syndrome (CRPS) involves pain usually in an arm or leg, usually after an injury, that’s significantly greater than it should be. In some people, the pain goes away as they heal, while in others it continues and becomes chronic. CRPS can involve sensory changes, abnormal temperature of the arm or leg, impaired movement, changes in the hair and skin, swelling, and changes in sweating.

CRPS has two main chronic types under the ICD-11:

• CRPS type I: This is due to some illnesses or injury, especially limb fracture or soft tissue injury that doesn’t involve direct nerve damage. About 90% of CRPS is this type.
• CRPS type II: This is due to nerve injury in your arm or leg, with pain spreading beyond the area controlled by the damaged nerve. 

Chronic Primary Headache and Orofacial Pain

This category covers several types of pain in the head, face, and mouth that last for at least two hours per day. It includes:

• Chronic migraine: Headache must occur 15 or more days each month for at least three months, include migraine symptoms at least eight days a month, and not stem from overuse of a medication.
• Chronic tension headache: This refers to daily or frequent headaches, usually on both sides, with a squeezing or tightening sensation lasting hours or days, and don’t get worse with routine physical activity.
• Burning mouth syndrome: This refers to a burning sensation occurring for more than two hours per day on at least 50% of the days over a three-month period.
• Chronic primary temporomandibular disorder (TMJ): This is a chronic form of jaw pain related to the muscles used to chew or the temporomandibular joint, which attaches the jaw to the skull.

This subgroup doesn’t include other headache disorders, which are categorized elsewhere in the ICD-11.

Chronic Primary Visceral Pain

Chronic primary visceral pain is in the trunk of your body and stems from specific internal organs. It’s considered synonymous with:

• Chronic primary chest pain syndrome
• Chronic pelvic pain syndrome
• Chronic primary epigastric pain syndrome
• Chronic primary painful bladder syndrome and interstitial cystitis
• Chronic primary abdominal pain syndrome

While the pain can be associated with any organ, the main diagnosis under this subtype is irritable bowel syndrome (IBS). IBS involves abdominal pain and discomfort that’s associated with bowel movements or changes in bowel habits, including diarrhea, constipation, or both of them alternating. Other symptoms include gas and bloating.

Chronic Primary Musculoskeletal Pain

Chronic primary musculoskeletal pain is in the muscles, bones, joints, and tendons. This diagnosis includes chronic, primary forms of:

• Low back pain
• Cervical pain
• Thoracic pain
• Limb pain

Chronic Secondary Pain

Chronic secondary pain isn’t a diagnosis on its own but instead an umbrella term for all the categories of nonprimary pain. These include:

• Chronic cancer-related pain
• Chronic postsurgical or post-traumatic pain
• Chronic secondary musculoskeletal pain
• Chronic secondary visceral pain
• Chronic neuropathic pain
• Chronic secondary headache or orofacial pain

Chronic Cancer-Related Pain 

Chronic cancer-related pain can be caused by:

• Cancerous tumors
• Metastases (cancer that has spread to different areas)
• Cancer treatment (chronic post-cancer treatment pain)

Chronic Postsurgical or Post-Traumatic Pain

These types of pain develop or get more intense after a surgery or tissue injury, including burns, and linger for at least three months after the surgery or injury. The pain may only be at the site of the trauma, in the territory of a damaged nerve, or related to nerves that come from the same spinal root.

Common causes of chronic postsurgical pain include:

• Spinal surgery
• Herniotomy
• Hysterectomy
• Amputation
• Thoracotomy
• Breast surgery
• Arthroplasty

Common causes of chronic post-traumatic pain include:

• Burns
• Whiplash
• Musculoskeletal injury

Chronic Secondary Musculoskeletal Pain

Chronic secondary musculoskeletal pain comes from the bones, joints, muscles, spine, and related soft tissues. It may be caused by local or systemic conditions, and pain may be induced by movement or happen spontaneously.

Subgroups of this diagnosis include pain from:

• Persistent inflammation, such as from an autoimmune disease
• Structural changes, such as from osteoarthritis (wear-and-tear arthritis) or spondylosis (age-related degeneration of the spine)
• Diseases of the nervous system, including multiple sclerosis, Parkinson’s disease, and peripheral neuropathy

Chronic Secondary Visceral Pain

Chronic secondary visceral pain comes from internal organs. It may be caused by:

• Mechanical factors, such as kidney stones, intestinal blockage, or restricted blood flow, or compression of internal organs
• Vascular mechanisms, which include altered blood flow to the internal organs
• Persistent inflammation in the internal organs

This category does not include neuropathic pain or visceral cancer pain.

Chronic Neuropathic Pain

Chronic neuropathic pain is due to a lesion or disease of the part of your nervous system that deals with sensory information (the somatosensory nervous system). It can be evoked by certain stimuli or occur spontaneously and may involve hyperalgesia (an exaggerated sensation to a painful stimulus) or allodynia (a sensation of pain caused by a nonpainful stimulus).

This diagnosis requires a history of disease or injury to the nervous system and a pain pattern that makes sense given the location of the damage. Chronic neuropathic pain can be: 

• Central, meaning that it stems from the central nervous system (brain and nerves of the spinal cord)
• Peripheral, meaning that it comes from the peripheral nervous system (the nerves of the arms and legs)

Chronic central neuropathic pain may be caused by:

• Spinal cord injury
• Brain injury
• Stroke
• Multiple sclerosis

Chronic peripheral neuropathic pain may be caused by:

• Peripheral nerve injury
• Polyneuropathy (degeneration of peripheral nerves)
• Radiculopathy (pinched nerve root at the spinal column)

Chronic Secondary Headache or Orofacial Pain

This classification includes all secondary head, face, and mouth pain that’s occurred for at least three months, on 50% of the days, for at least two hours a day. Subtypes include:

• Chronic secondary orofacial pain
• Chronic dental pain (involving teeth or tissues of the mouth), including that from cavities or trauma to a tooth
• Chronic neuropathic orofacial pain, including trigeminal neuralgia (severe pain from a nerve in the face)
• Headache or orofacial pain attributed to chronic secondary temporomandibular disorders, which may be due to inflammation, injury, or a nervous system disease

A Word From Verywell

While some members of the medical community still object to the classification of chronic pain as a disease in its own right, many others embrace these diagnoses and the improved clarity they provide. Their inclusion in the ICD-11 is a step forward for the millions of people who live with chronic pain and the medical practitioners who treat them.