ABPMR Pain Medicine cheat sheet

Primary afferents: A-delta fibers are thinly myelinated and conduct sharp first pain at roughly 5-30 m/s; C fibers are unmyelinated, conduct dull second pain below 2 m/s, and are polymodal.

Nociceptive pathway: dorsal root ganglion to dorsal horn synapses in laminae I, II, and V, then decussation in the anterior white commissure within 1-2 segments, then the lateral spinothalamic tract to thalamus and somatosensory cortex.

Gate control: large A-beta afferent input excites inhibitory interneurons in the dorsal horn and decreases projection-neuron firing, the physiologic basis for TENS and counterirritation.

Descending modulation: periaqueductal gray excites the rostral ventromedial medulla, which releases serotonin and norepinephrine in the dorsal horn; serotonin-norepinephrine reuptake inhibitors amplify this pathway.

Mu opioid receptor activation produces analgesia, miosis, respiratory depression, euphoria, constipation, and dependence; kappa activation produces spinal analgesia with dysphoria and diuresis.

NSAIDs inhibit cyclooxygenase and lower prostaglandin synthesis; they show a ceiling effect for analgesia and carry dose-related risks of GI bleeding, acute kidney injury, and hypertension.

Local anesthetics are weak bases that block voltage-gated sodium channels from the cytoplasmic side; higher pKa slows onset, and the acidic pH of inflamed or infected tissue reduces the uncharged fraction and blunts the block.

Neuropathic pain reflects a lesion or disease of the somatosensory system and is suggested by burning or electric-shock pain, allodynia, hyperalgesia, and sensory loss in a neuroanatomic distribution.

Red flags mandating prompt imaging or urgent referral: fever, unexplained weight loss, night or rest pain, cancer history, intravenous drug use, trauma, progressive motor deficit, saddle anesthesia, and bowel or bladder dysfunction.

Acute low back pain without red flags does not require routine imaging in the first 4-6 weeks, since early MRI raises costs without improving outcomes.

Straight leg raise: pain reproduced between 30 and 70 degrees of passive hip flexion with the knee extended suggests L5 or S1 root irritation; the crossed straight leg raise is more specific but less sensitive.

Spurling test (cervical extension, ipsilateral rotation, axial compression) is highly specific for cervical radiculopathy; the shoulder abduction relief sign also supports cervical root involvement.

Neuropathic screening: a DN4 score of 4 or more out of 10, or a positive LANSS, supports a neuropathic mechanism and guides choice of gabapentinoid, duloxetine, or tricyclic.

Neurogenic claudication is provoked by walking and relieved by sitting or forward flexion, whereas vascular claudication is relieved by standing still and is not altered by posture.

Visceral referred pain follows convergence of visceral and somatic afferents onto shared spinal segments, producing pain in a remote dermatome, such as gallbladder pain referred to the right shoulder via C3-C5.

Sacroiliac dysfunction screening uses the FABER (Patrick) test plus provocation tests; facet-mediated pain is suggested by paraspinal tenderness that worsens with extension and rotation and eases with flexion.

Cervical transforaminal epidural injection carries a rare but catastrophic risk of spinal cord or brainstem infarction from vertebral artery injury or embolized particulate steroid; non-particulate dexamethasone is preferred.

Facet joint pain is diagnosed with medial branch blocks; at least 50% pain relief on two concordant blocks is the usual criterion before radiofrequency neurotomy.

Radiofrequency neurotomy yields median relief of roughly 6-12 months for lumbar facet pain and can be repeated when pain returns with the same diagnostic response.

Stellate ganglion block is performed at the C6 level (Chassaignac tubercle) with the needle directed to the anterior aspect of the longus colli; ipsilateral Horner syndrome confirms sympathetic blockade.

Lumbar sympathetic block targets the L2-L3 level for complex regional pain syndrome of the lower limb; the cervical and upper thoracic chain is targeted for upper limb involvement.

Spinal cord stimulation requires a successful trial, typically 50% or greater pain reduction, before permanent implantation and is best supported for failed back surgery syndrome and complex regional pain syndrome.

Per ASRA guidance, most joint and soft tissue injections may proceed without stopping aspirin or NSAIDs, whereas warfarin, direct oral anticoagulants, and clopidogrel require timed interruption.

Absolute contraindications to interventional pain procedures include infection at the site, uncorrected coagulopathy, patient refusal, and allergy to a required agent; pregnancy adds fluoroscopic risk.

Acetaminophen ceiling: total adult daily dose is limited to 3-4 g, and 2-3 g is advised with liver disease or chronic alcohol use; hepatic necrosis is dose dependent.

Opioid initiation: start a short-acting agent at the lowest effective dose, check the prescription drug monitoring program, and offer naloxone when the dose reaches 50 morphine milligram equivalents per day or risk factors coexist.

Approximate morphine milligram equivalents: 30 mg oral morphine equals 20 mg oxycodone, 30 mg hydrocodone, or 7.5 mg hydromorphone; methadone conversion is nonlinear and dose dependent.

Gabapentin and pregabalin bind the alpha-2-delta subunit of voltage-gated calcium channels, reduce excitatory transmitter release, require renal dose adjustment, and are first-line for neuropathic pain.

Duloxetine, a serotonin-norepinephrine reuptake inhibitor, is approved for diabetic peripheral neuropathic pain, fibromyalgia, and chronic musculoskeletal pain; analgesia is independent of mood effect but blood pressure should be monitored.

Tricyclics remain effective for neuropathic pain; amitriptyline is more anticholinergic and sedating than nortriptyline or desipramine, and all are contraindicated after recent myocardial infarction.

Topical lidocaine 5% patch is indicated for postherpetic neuralgia with minimal systemic absorption; capsaicin 8% requires pretreatment and gives prolonged relief by defunctionalizing TRPV1 nociceptors.

Triptans are contraindicated in ischemic heart disease, uncontrolled hypertension, and hemiplegic or basilar migraine, and should not be used within 24 hours of another triptan or an ergot.

The biopsychosocial model treats pain as the product of biological, psychological, and social factors; outcomes improve when all three are addressed rather than nociception alone.

Yellow flags predicting chronicity include catastrophizing, fear-avoidance beliefs, anxiety, depression, low work satisfaction, and compensation issues; they differ from red flags, which suggest serious pathology.

Cognitive behavioral therapy targets maladaptive thoughts and behaviors through cognitive restructuring, relaxation training, and behavioral activation, improving function, mood, and coping in chronic pain.

Graded exposure and graded activity replace pain-contingent rest with quota-based, time-contingent progression, reducing fear-avoidance, disuse, and repeated flare cycles.

Interdisciplinary functional restoration combines physical conditioning, occupational therapy, psychological intervention, and vocational planning; it yields the best return-to-work outcomes in chronic disabling pain.

Exercise is a core intervention in chronic musculoskeletal pain: it improves strength, function, and pain tolerance, and benefit grows with adherence rather than with any single exercise modality.

Sleep disturbance amplifies central sensitization; sleep hygiene, stimulus control, and cognitive behavioral therapy for insomnia are first-line, with sedatives used cautiously in older adults because of fall and confusion risk.