Overview notes of pain modulation pathways

On my first day at School of Medicine and Pharmacology, Stephan whisked me off to a Clinical Masterclass presented by visiting international experts Ralf Baron and Anthony Dickinson.

Each of their introductions gave me a great overview of pain modulation pathways and associated conditions.

Some of my sketch (y) day-one notes are below:

Types of chronic pain

Nociceptive – arthritis, ischema, visceral

Neuropathic (nerve lesion) – postherpetic neuralgia, post traumatic neuralgia,  diabetic neuropathy.

Each of these can be experienced through different feelings/sensations. Some conditions can have a a combination of both types eg low back pain, radiculopathy, tumour, Chronic Regional Pain Syndrome.

Nerve lesion types: focal nerve lesion (phantom pain, cancer associated infiltration of the nerve); general nerve lesion (polyneuropathy); central lesion (stroke, spinal chord).

Neuropathic pain might have negative symptoms or sensory deficits across all modalities or positive symptoms such as prickling burning, allodynia.

Can symptoms be linked to mechanisms?

Is there a sensory phenotype?

A Neuropahic Pain Symptom Inventory is used with a scoring system:



sensitivity to touch

cold or hot



light pressure

For patients who are heterogeneous – have medical conditions with several causes they looked for:

Preserved innervation – sensitisation, burning, allodynia, attack, pressure

Loss of Innervation -burning, pricking numbness

Sensory phenotype could be used as an assessment, diagnostic, and treatment tool.


Pain fibres change their phenotype with a lesion ie sodium expression leads to ectopic activity equals shooting feelings.


Constant input to C fibres will activate A fibres and then a synaptic switch to A fibre activity.


Limbic Brain  (ancient) = affective aspects of pain – fear, anxiety sleep

Cortex (newer in evolutionary terms) = location and intensity


Pain types and chemical chain reactions:

Nociceptive – tissues – chemical activation of prostaglandins

Neuropathic – nerves – activation of ion channels


You can inhibit pain with another pain type with a reduction in perceived pain of 30%. If you stub your toe, to reduce that pain, bite your thumb.









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