⭐ What is pain?
According to International Association for the Study of Pain (IASP), pain is
“An unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage”
Indeed, pain is related to both physical and mental experience. Pain doesn’t just mean it’s harmful to a person, it plays multiple roles for everyone. Pain can be encouraging, protecting and hurting the individual.
Two people seeing the same picture of a bleeding wound won’t feel the same degree of pain. Because the interpretation of the sensation is based on their unique life experience, as well as cultural expectation. Therefore,
Every individual’s pain should be respected !
You might learn the news about professional athletes battled through severe injuries in an important game. In fact, pain can be alleviated (temporally) with strong emotion or distracting yourself from the unpleasant feeling. However, your pain can also be aggravated with negative mental state, which becomes a vicious cycle because the obnoxious sensation leads to worse emotion.
⭐ How do you feel pain?
Human body takes mainly two kinds of somatosensory input: Innocuous vs. Nocuous stimulation. The former is the sensation like touch, itchiness, warmth and coldness; the later can be burning, freezing, piercing or stretching sensation that triggers pain.
These sensory inputs are detected by your sensory neurons, then transferred to the dorsal horn of spinal cord. From spinal cord they diverge to two routes, one goes straight to the thalamus; and the other one passes through brainstem then the thalamus.
Eventually, all inputs are transported to your brain (somatic or cognitive-emotional brain), which discriminates the types of stimuli and interprets it into psychological reaction.
Harrison and Field suggested there are four factors affecting pain after stroke, this concept is nicely aligned with the holistic view in occupational therapy:
1. Psychological: depression, anxiety, stress and loneliness.
2. Central neuropathic: altered pain threshold, maladaptive plasticity.
3. Autonomic: sympathetically maintained pain.
4. Peripheral injuries: trauma, inflammation, soft tissue swelling or degeneration…etc.
⭐ Common Pain Syndromes After Stroke
There are three stages after the onset of a stroke. Acute stage: 1-14 days; sub-acute stage: 14-90 days; chronic stage: more than 90 days.
Studies showed about 14-38% of acute patients had at least one pain syndrome, which increased to around 42% in sub-acute stage. Finally, approximately 32-46% of patients in chronic stage suffered pain syndrome.
1. Muscular-skeletal Pain (shoulder excluded)
The most common pain syndrome after stroke, especially in sub-acute stage (>30%). Usually this is the stage when patients become more stable and can start therapeutic activities, which could cause muscle soreness and micro-trauma to soft tissue. Such pain reaction is well expected and actually beneficial for motor recovery.
2. Hemiplegic Shoulder Pain (HSP)
The second most common pain syndrome, it also happens more often after sub-acute stage (around 15%). HSP may be caused by activities or other complications (such as shoulder muscle weakness) after stroke. We will illustrate it more in another article.
3. Central Post-stroke Pain (CPSP)
Patients feel severely uncomfortable sensation (burning, stabbing or shooting pain) even with light stimulation (gentle touch or stroking). CPSP happens in about 2-6% of stroke patients. In some patients, the affected hand can be red, swelling and warm, accompanied with strong shoulder pain, so called complex regional pain syndrome (CRPS) (we used to name it shoulder-hand syndrome). It is still unclear what caused CPSP.
Headache is more common in acute stage (5-33%), then the prevalence dropped below 23% in sub-acute and chronic stages.
5. Spasticity Related Pain
Spasticity is an involuntary muscle activity due to neuromuscular malfunction after brain injury. Spasticity may lead to prolong muscle tension and poor posture, which can cause pain. In 2015, a study found that only sub-acute and chronic stage patients had spasticity related pain (0.9% and 4.3%). However, it is still unclear if spasticity has a direct or indirect effect on pain.
6. Other Types of Pain
We should also consider that most stroke patients were middle aged or elderly people, almost half (49%) of the population lives with pain even before the onset. An Australian study (2015) indicated people who were suffering shoulder problems before stroke, had 7 times higher risk of developing HSP. Therefore, pain can also relate to the individual’s pre-existing injuries, poor posture, occupation and daily living habits.
Pain is not just about physical injury, we should always be aware of psychological and social factors. Stroke has tremendous impacts on the patient and families, in the process of recovery and adaptation, the complications also makes it challenging to understand pain syndromes after the onset.
In order to treat pain after stroke, it is important to begin with muscular-skeletal and soft tissue system, then study the neurological and psychological factors, also including the person’s unique life experience.
Overall, we should always try to understand the individual holistically, then investigate their pain.
2. Bushnell et al., Cognitive and emotional control of pain and its disruption in chronic pain. Nat Rev Neurosci. 2013;14(7):502–511.
3. Kuner & Flor, Structural plasticity and reorganisation in chronic pain. Nat Rev Neurosci. 2017;18(1):20–30.
4. Harrison & Field, Post stroke pain: identification, assessment, and therapy. Cerebrovasc Dis. 2015;39(3–4):190–201.
5. Ong et al., Role of the prefrontal cortex in pain processing. Mol Neurobiol. 2019;56(2):1137–1166.
6. Gierthmühlen et al., Mechanism-based treatment in complex regional pain syndromes. Nat Rev Neurol. 2014;10(9):518–528.
7. Hansen et al., Pain following stroke: a prospective study. Eur J Pain. 2012;16(8):1128–1136.
8. Paolucci et al., Prevalence and time course of post-stroke pain: a multicenter prospective hospital-based study. Pain Med. 2016;17(5):924–930.
9. Liampas et al., Prevalence and management challenges in central post-stroke neuropathic pain: a systematic review and meta-analysis. Adv Ther. 2020;37(7):3278–3291.
10. Krause et al., The cortical signature of central poststroke pain: gray matter decreases in somatosensory, insular, and prefrontal cortices. Cereb Cortex. 2016;26(1):80–88.
11. Sheean D.G. Is spasticity painful? Eur J Neurol. 2009;16(2):157–158.
12. Adey-Wakeling et al., Incidence and associations of hemiplegic shoulder pain poststroke: prospective population-based study. Arch Phys Med Rehabil. 2015;96(2):241–247.e1.