TYPES OF PAIN

Author: Jeshnu Tople

International association for study of pain (IASP) defined pain as ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.’¹

Classification based on time:

ACUTE PAIN

It is defined as the pain which lasts for less than 3 months or which is directly related to tissue damage. Ex- post operative pain, traumatic pain.¹

Duarte² defines acute pain as temporarily related to injury and that resolves during the appropriate healing period. It often responds to treatment with analgesic medications and treatment of precipitating cause. Characteristics include:

• Short lived, less than 3 months
• Varying intensity, initially severe then subsidises as healing takes place
• Intact nervous system usually
• Reason can be pinpointed
• Responds well to conventional analgesics
• Psychological problems such as depression are short lived if present at all.

CHRONIC PAIN

IASP defined it as pain persistent more than 3 months. However pain more than 6 months’ duration also is defined as chronic pain.¹ It is further classified as following.^3,4

I. Chronic primary pain

It is the pain in one or more anatomic regions that persists or recurs for longer than 3 months and is associated with significant emotional distress or significant functional disability (interference with activities of daily life and participation in social roles) and that cannot be better explained by another chronic pain condition. It can be-

1. Chronic widespread pain
2. Complex regional pain syndrome
3. Chronic primary headache and orofaacial pain
4. Chronic primary visceral pain
5. Chronic primary musculoskeletal pain other than orofacial

II. Chronic cancer-related pain

It includes pain caused by the cancer itself and pain caused by the cancer treatment. It may be continuous or intermittent. It is subdivided as:

1. Chronic cancer pain
2. Chronic post-chemotherapy pain
3. Chronic post-radiotherapy pain

III. Chronic postsurgical and posttraumatic pain

This is defined as pain that develops after a surgical procedure or a tissue injury (involving any trauma, including burns) and persists at least 3 months after surgery or tissue trauma. This is a definition of exclusion, as all other causes of pain (infection, recurring malignancy) as well as pain from a pre-existing pain problem need to be excluded.

IV. Chronic neuropathic pain

It is caused by a lesion or disease of the somatosensory nervous system. Neuropathic pain may be spontaneous or evoked. For it to occur there must be the lesion or disease involving the nervous system. Negative or positive sensory signs compatible with the innervation territory of the lesioned nervous structure must be present. It can be peripheral or central neuropathic pain.

V. Chronic secondary headache and orofacial pain

Chronic headache and chronic orofacial pain is defined as headaches or orofacial pains that occur on at least 50% of the days during at least 3 months. It is further divided as:

1. Headache or orofacial pain attributed to various causes
2. Chronic dental pain
3. Chronic headache/orofacial neuropathic pain
4. Headache/orofacial pain attributrd to chronic secondary temporomandibular disorders

VI. Chronic visceral pain

Chronic visceral pain is persistent or recurrent pain that originates from the internal organs of the head and neck region and the thoracic, abdominal, and pelvic cavities.The pain is usually perceived in the somatic tissues of the body wall (skin, subcutis, muscle) in areas that receive the same sensory innervation as the internal organ at the origin of the symptom (referred visceral pain). In these areas, secondary hyperalgesia often occur; the intensity of the symptom may bear no relationship with the extent of the internal damage or noxious visceral stimulation. It can be due to

1. persistent inflammation
2. vascular mechanisms (ischemia, thrombosis)
3. mechanical factors (obstruction and distension, traction and compression)
4. combined mechanisms (eg, obstruction and inflammation concurrently).

VII. Chronic musculoskeletal pain

It is defined as persistent or recurrent pain that arises as part of a disease process directly affecting bone(s), joint(s), muscle(s), or related soft tissue(s). It may arise from persistent inflammation or associated with structural changes or with diseases of nervous tissue.

Classification based on mechanism¹

Nociceptive Pain

Pain that arises from actual or threatened damage to nonneural tissue and is due to activation of nociceptors. Inflammatory pain is a sub-type of nociceptive pain.

Neuropathic Pain

Pain caused by lesion or disease of somatosensory nervous system. Subtype of neuropathic pain  are neuritis, neuralgia, peripheral neuropathy etc. Neuraligia is along the distribution of nerve or nerves. Neuritis is the inflammation of nerve or nerves.

References:

1. Das G. Basic of pain management.CBS Publishers & distributers; 2017.
2. Acute Postoperative Pain: Definition of Acute Pain | Pain Community Centre [Internet]. Paincommunitycentre.org. 2018 [cited 8 July 2018]. Available from: http://www.paincommunitycentre.org/article/acute-postoperative-pain-definition-acute-pain.
3. Treede R, Rief W, Barke A, Aziz Q, Bennett M, Benoliel R et al. A classification of chronic pain for ICD-11. PAIN. 2015:1.
4. Barke A, Rief W, Treede R & The IASP Task Force Chronic Pain Classification for ICD-11. A Classification of Chronic Pain Syndromes for ICD-11 [document on the Internet] Available from: https://videnomsmerter.files.wordpress.com/2016/10/poster_chronic_pain_classification_icd-11.pdf