Nociceptive Pain

Nociceptive pain, the most common type of pain, is defined by the International Association for the Study of Pain (IASP) as “pain that arises from actual or threatened damage to non-neural tissue and is due to activation of nociceptors” 

Nociceptive pain is a nervous system response that is our physiological mechanism to prevent injury when we move our hand away from a hot stove top or to help recover from injury when we rest an injured extremity. However, nociceptive pain after trauma or surgery can be debilitating and often requires treatment to enhance recovery after trauma and surgery. Nociceptive pain can be acute pain or become chronic pain.

Nociceptive Pain is often further divided as either somatic or visceral pain.

Somatic pain is due to stimulation of peripheral nociceptors capable of responding to stimuli such as mechanical (pressure), thermal, chemical and other stimulation. It most most commonly described as sharp, localized pain that is predominately being carried by fast, myelinated Aδ-fibers.

Examples of somatic nociceptive pain:

• Burn
• Fractures
• Incisions, Wounds
• Cellulitis
• Shingles
• Arthritis
• Gout
• Musculo-skeletal Pain

Visceral pain originating from viscera, muscles, and bone is described as dull and diffuse and often poorly localized. It is frequently mediated by the slower, small unmyelinated C-fibers. Visceral pain is often perceived as more unpleasant than somatic pain.

Examples for visceral nociceptive pain:

• Tumor invasion
• Obstructions (bowel, ureter, bile duct)
• Colic
• Angina
• Pancreatitis

Neuropathic Pain

Neuropathic pain has been defined by the IASP as “pain arising as a direct consequence of a lesion or disease affecting the somatosensory system”. It requires damage to peripheral or central nerves. Neuropathic pain is very often chronic pain.

Examples of neuropathic pain:

• Peripheral neuropathy (diabetes, HIV, chemotherapy, radiation treatment)
• Neuralgia (e.g trigeminal neuralgia)
• Spinal cord compression
• Plexopathy

Nociplastic Pain

The initial binary classification of pain left many patients unclassified: there are patients who present with both nociceptive and neuropathic symptoms, as well as patients who do not exhibit either signs or symptoms of any actual or threatened tissue damage, nor evidence of a lesion or disease of the somatosensory system.

There has been a bit of a debate regarding how to best classify and label the mechanisms that did not fit neatly into either the drawer of nociceptive or neuropathic pain. Terms sich as  ‘idiopathic pain’, functional pain’, ‘centralized pain’, ‘central sensitization’, and ‘central hypersensitivity’ had been proposed, when in 2017, the IASP Council adopted the term “nociplastic pain” as a third mechanistic descriptor of chronic pain. It is now defined as  “pain that arises from altered nociception despite no clear evidence of actual or threatened tissue damage causing the activation of peripheral nociceptors or evidence for disease or lesion of the somatosensory system causing the pain”.

Mixed Pain

Another frequently used terminology is the term “mixed pain.” This term is increasingly used but has not been adopted by the IASP. The common definition of mixed pain is a pain with “an overlap of nociceptive and neuropathic symptoms”.

Pain syndromes that have been discussed to represent mixed pain states:

• Cancer pain
• Lower back pain,
• Osteoarthritis pain
• Persistent Postsurgical pain

Examples of nociplastic pain:

• Fibromyalgia
• Complex regional pain syndrome type 1
• Irritable bowel syndrome 
• Bladder pain syndrome