Types and theories of pain — practice questions

(a) Classification and explanation:

• Sam now has chronic pain — persisting beyond normal healing time (>3–6 months) despite resolved tissue damage.
• Pain has become decoupled from nociception — nervous system maintains pain signals without ongoing injury.
• Possible central sensitisation — spinal cord and brain amplify pain signals.

(b) Gate control theory applied:

• Pain impulses travel via small-diameter A-delta and C fibres to substantia gelatinosa in spinal cord.
• In Sam's case, the gate is chronically open — brain descending pathways (anxiety, focus on pain) fail to close it.
• Negative mood and attention to pain (psychological factors) keep gate open even without peripheral input.
• Explains why TENS (large fibre stimulation) and distraction may help — competing input closes gate.

(c) Evaluation of biopsychosocial model:

• Strengths: Integrates Melzack & Wall gate theory with psychological (catastrophising, depression) and social (work loss, disability benefits) factors — matches Sam's profile.
• Holistic: Avoids telling patients pain is "all in the head" — acknowledges real neurobiological changes in chronic pain.
• Clinical utility: Underpins multimodal pain clinics combining medication, CBT, and physiotherapy (see 3.3.3).
• Limitations:
  • Vague — difficult to test as a unified model; which component dominates varies by patient.
  • Individual responsibility — may blame patient for "psychological" contribution.
  • Does not fully explain neuropathic pain mechanisms at molecular level.

Judgement: Superior to purely biomedical model for chronic pain, but treatment still requires targeting each component specifically.

(a) Calculation of Percentage Pain Reduction:

1. Identify initial and final values:

   • Initial Pain Score (NRS_initial) = 8
   • Final Pain Score (NRS_final) = 5

2. Calculate the absolute reduction:

   • Reduction = NRS_initial - NRS_final
   • Reduction = 8 - 5 = 3 points

3. Apply the percentage change formula:

   • Percentage Reduction = (Absolute Reduction / Initial Score) × 100%
   • Percentage Reduction = (3 / 8) × 100%

4. Calculate the final answer:

   • Percentage Reduction = 0.375 × 100% = 37.5%

   Answer: The patient reported a 37.5% reduction in pain.

(b) Biopsychosocial Explanation:

The 37.5% reduction in pain can be attributed to the interaction of the three components of the biopsychosocial model, targeted by a multidisciplinary programme:

• Biological: The programme likely included physiotherapy to strengthen muscles around the knee joint, improving stability and reducing physical stress. This also stimulates large A-beta nerve fibres, which, according to Gate Control Theory, helps to 'close the gate' to pain signals.

• Psychological: The programme may have involved Cognitive Behavioural Therapy (CBT) to help the patient reframe negative thoughts about their pain (e.g., catastrophising). By learning coping strategies and reducing fear-avoidance behaviours, the patient's descending control from the brain can modulate the pain gate more effectively, reducing the perceived intensity of the pain.

• Social: Group sessions or peer support elements of the programme would address social isolation often linked with chronic pain. Sharing experiences and receiving validation can improve mood and provide a sense of agency, which are social factors that buffer against the psychological distress of pain.