Residency · Residency · Internal Medicine

Chronic Pain Management: A Multimodal Approach

Introduction

Chronic pain, defined as pain persisting beyond 3 months, affects over 50 million US adults and is the leading cause of disability worldwide. The failed paradigm of opioid-centric pain management contributed to an ongoing addiction and overdose crisis. Modern pain management emphasizes a biopsychosocial model with multimodal therapies targeting the physical, psychological, and social dimensions of pain. Internal medicine residents must be comfortable initiating evidence-based non-opioid therapies and managing opioids safely when indicated.

Pain Neuroscience

• Nociceptive pain: caused by tissue damage activating peripheral nociceptors (somatic or visceral)
• Neuropathic pain: caused by lesion or disease of the somatosensory nervous system (burning, shooting, tingling)
• Nociplastic pain (central sensitization): amplified central nervous system processing without clear nociceptive input (fibromyalgia, chronic widespread pain, irritable bowel syndrome)
• Peripheral and central sensitization: repeated nociceptive input leads to reduced pain thresholds, expanded receptive fields, and pain from normally non-painful stimuli (allodynia)
• Identifying the pain mechanism guides pharmacotherapy selection

Assessment

• Pain history: location, quality, intensity (0-10 NRS), temporal pattern, aggravating/alleviating factors, prior treatments
• Functional impact: PEG scale (Pain, Enjoyment of life, General activity); functional goals are more meaningful than pain scores
• Psychosocial assessment: depression, anxiety, catastrophizing, social isolation, adverse childhood experiences
• Screen for substance use disorder: Opioid Risk Tool (ORT), SOAPP-R; urine drug testing
• Red flags: unexplained weight loss, fever, neurologic deficits, progressive weakness (evaluate for malignancy, infection, cauda equina)

Non-Pharmacologic Therapies

Physical and Rehabilitative

• Exercise therapy: strongest evidence base; aerobic exercise, resistance training, yoga, tai chi all reduce pain and improve function in chronic low back pain, osteoarthritis, and fibromyalgia
• Physical therapy: graded exercise programs, manual therapy, activity modification
• Cognitive behavioral therapy (CBT): restructures maladaptive pain beliefs and catastrophizing; NNT of 2-4 for clinically meaningful improvement
• Acceptance and commitment therapy (ACT): emphasizes psychological flexibility and value-based living despite pain
• Mindfulness-based stress reduction (MBSR): demonstrated benefit in chronic low back pain (JAMA 2016)

Interventional Procedures

• Epidural steroid injections: short-term relief for lumbar radiculopathy; limited evidence for long-term benefit
• Facet joint interventions: medial branch blocks followed by radiofrequency ablation for facet-mediated pain
• Spinal cord stimulation: for failed back surgery syndrome and complex regional pain syndrome
• Trigger point injections: for myofascial pain syndrome
• Nerve blocks: peripheral nerve blocks for localized neuropathic pain

Non-Opioid Pharmacotherapy

First-Line Agents by Pain Type

Neuropathic Pain

• Gabapentinoids: gabapentin (300-3600 mg/day), pregabalin (150-600 mg/day); NNT 6-7 for 50% pain relief
• SNRIs: duloxetine (60-120 mg/day), venlafaxine (150-225 mg/day); also effective for comorbid depression
• Tricyclic antidepressants: amitriptyline, nortriptyline (25-150 mg at bedtime); NNT 3-4; anticholinergic side effects limit use in elderly
• Topical lidocaine (5% patch): for localized neuropathic pain, minimal systemic absorption
• Topical capsaicin (8% patch): for postherpetic neuralgia, HIV-associated neuropathy

Musculoskeletal Pain

• Acetaminophen: up to 2 g/day in chronic use (reduced ceiling to protect against hepatotoxicity)
• NSAIDs: use lowest effective dose for shortest duration; topical NSAIDs (diclofenac gel) preferred for localized osteoarthritis (comparable efficacy, fewer systemic effects)
• Duloxetine: FDA-approved for chronic musculoskeletal pain and osteoarthritis
• Cyclobenzaprine: short-term use for acute muscle spasm; avoid chronic use

Nociplastic Pain (Fibromyalgia)

• Duloxetine (60-120 mg/day): FDA-approved for fibromyalgia
• Pregabalin (300-450 mg/day): FDA-approved for fibromyalgia
• Milnacipran (100-200 mg/day): FDA-approved for fibromyalgia
• Low-dose naltrexone (1.5-4.5 mg/day): emerging evidence for fibromyalgia and central sensitization

Opioid Therapy: When and How

Indications

• Moderate-to-severe pain significantly impairing function despite optimized non-opioid multimodal therapy
• Cancer pain, palliative care, and end-of-life care
• Chronic non-cancer pain: opioids should be a last resort, not a first-line therapy

Safe Prescribing Practices (CDC 2022 Guideline)

• Start with immediate-release opioids at lowest effective dose
• Avoid exceeding 50 morphine milligram equivalents (MME)/day without careful reassessment; use extreme caution above 90 MME/day
• Co-prescribe naloxone for all patients receiving >= 50 MME/day, history of overdose, concurrent benzodiazepine use, or substance use disorder history
• Prescription drug monitoring program (PDMP): check before every new opioid prescription and periodically thereafter
• Urine drug testing: baseline and at least annually; confirm expected drug presence and absence of undisclosed substances
• Reassess opioid benefit every 1-3 months; taper if risks outweigh benefits

Opioid Tapering

• Gradual taper: reduce by 10% of total daily dose per month
• Avoid abrupt discontinuation (risk of withdrawal, destabilization, illicit opioid use)
• Optimize non-opioid pain management before and during taper
• Collaborate with addiction medicine if opioid use disorder is identified

Opioid Use Disorder

• Screen for OUD using DSM-5 criteria
• Medication-assisted treatment (MAT): buprenorphine/naloxone or methadone; reduces mortality by 50%
• Internal medicine residents should obtain X-waiver training (now eliminated; all DEA-registered providers can prescribe buprenorphine)

Key Clinical Pearls

• Identify the pain mechanism (nociceptive, neuropathic, or nociplastic) to guide pharmacotherapy selection
• Exercise and CBT have the strongest evidence for chronic pain and should be prescribed alongside pharmacotherapy
• Duloxetine is the most versatile non-opioid analgesic, with FDA approval for neuropathic pain, fibromyalgia, chronic musculoskeletal pain, and osteoarthritis
• All providers with a DEA license can now prescribe buprenorphine for opioid use disorder; there is no longer a separate waiver requirement

References

1. Dowell D, Ragan KR, Jones CM, et al. CDC Clinical Practice Guideline for Prescribing Opioids for Pain -- United States, 2022. MMWR Recomm Rep. 2022;71(3):1-95.
2. Finnerup NB, Attal N, Haroutounian S, et al. Pharmacotherapy for Neuropathic Pain in Adults: A Systematic Review and Meta-Analysis. Lancet Neurol. 2015;14(2):162-173.
3. Cherkin DC, Sherman KJ, Balderson BH, et al. Effect of Mindfulness-Based Stress Reduction vs Cognitive Behavioral Therapy on Back Pain and Functional Limitations. JAMA. 2016;315(12):1240-1249.
4. Volkow ND, Blanco C. The Changing Opioid Crisis: Development, Challenges, and Opportunities. Mol Psychiatry. 2021;26(1):218-233.

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