What is the step‑by‑step algorithm for accurately diagnosing pain?

Algorithm for Accurate Pain Diagnosis

The correct pain diagnosis requires a systematic three-step approach: (1) comprehensive pain characterization through structured history, (2) focused physical and neurological examination to identify mechanism-specific signs, and (3) selective use of diagnostic imaging or investigations only when red flags are present or when clinical assessment suggests specific pathology requiring confirmation. 1

Step 1: Structured Pain History

Essential Pain Characteristics to Document

• Temporal features: Document onset (acute <4 weeks, subacute 4-12 weeks, chronic >12 weeks), duration, periodicity, and whether pain is continuous versus intermittent 2, 1
• Location and radiation patterns: Identify precise anatomical distribution and whether pain follows dermatomal or nerve territory patterns, as this guides mechanism identification 2, 1
• Quality descriptors: Aching, throbbing, or pressure suggests somatic nociceptive pain; cramping or gnawing indicates visceral nociceptive pain; shooting, sharp, or stabbing sensations point to neuropathic pain 1, 3
• Intensity measurement: Use validated scales (visual analog scale, numerical rating scale 0-10, or verbal rating scale) at every assessment 1
• Trigger and relieving factors: Document effects of hot/cold, sweet foods, prolonged chewing, eating, brushing teeth, touching the face, weather, physical activity, posture, stress, and tiredness 2, 1

Critical Red Flags Requiring Immediate Investigation

• Cauda equina syndrome indicators: Saddle anesthesia, bowel/bladder dysfunction, bilateral leg weakness 4
• Malignancy concerns: History of cancer, unexplained weight loss, age >50 with new-onset pain, pain at rest or night pain 4
• Infection signs: Fever, recent infection, immunosuppression, intravenous drug use 4
• Fracture risk: Significant trauma, osteoporosis, prolonged corticosteroid use, midline tenderness 4
• Progressive neurological deficits: Worsening motor weakness, sensory loss, or reflex changes 4

Functional and Psychosocial Assessment

• Functional interference: Evaluate pain impact on daily activities, work, social life, sleep, appetite, sexual functioning, and mood—this should guide treatment priorities more than intensity alone 1, 3
• Psychological screening: Screen for depression, anxiety, catastrophizing, fear-avoidance beliefs, and suicidal ideation, as these amplify pain perception and predict disability more strongly than pain intensity 4, 1
• Prior treatment response: Review all previous analgesics, their efficacy, tolerability, and reasons for discontinuation to avoid repeating ineffective therapies 1

Step 2: Focused Physical and Neurological Examination

Systematic Physical Assessment

• Visual inspection: Identify color changes, swelling, skin lesions, muscle atrophy, or deformities 2
• Palpation: Assess for tenderness, trigger points, muscle hypertrophy, joint crepitus, and localized warmth 2
• Range of motion: Document active and passive movement limitations, joint stability, and pain provocation with specific movements 2

Neurological Examination for Mechanism Identification

• Sensory testing: Assess sensitivity to pinprick, light touch, pressure, cold, heat, and vibration to identify positive (allodynia, hyperalgesia) or negative (hypoesthesia, anesthesia) sensory signs 5
• Motor examination: Test muscle strength, tone, and bulk; document any weakness or fasciculations 1
• Reflex testing: Evaluate deep tendon reflexes and pathological reflexes 1
• Provocative maneuvers: Perform straight leg raise for radiculopathy, FABER test for hip pathology, or specific joint stress tests as indicated by pain location 4
• Autonomic signs: Look for color changes, temperature differences, sweating abnormalities, or edema suggesting complex regional pain syndrome 5

Location-Specific Examination Priorities

• Right upper quadrant pain: Palpate for Murphy's sign, assess liver edge, evaluate for costovertebral angle tenderness 2
• Facial pain: Examine cranial nerves, palpate temporomandibular joint, assess muscles of mastication, perform intraoral examination for dental pathology 2
• Low back pain: Assess for midline tenderness (vertebral fracture), perform neurological examination including straight leg raise, evaluate gait 4

Step 3: Selective Diagnostic Imaging and Investigations

When to Order Imaging

Do NOT routinely image patients with nonspecific pain in the absence of red flags, as early imaging does not improve outcomes and leads to unnecessary procedures 4

Imaging Algorithm by Clinical Scenario

Acute abdominal pain:

• Right upper quadrant: Ultrasonography is the initial test of choice 2
• Right or left lower quadrant: Computed tomography is recommended 2
• Avoid conventional radiography due to limited diagnostic value 2

Low back pain:

• No imaging if no red flags and duration <4-6 weeks 4
• Plain radiography for suspected vertebral compression fracture or after 4-6 weeks of failed conservative therapy 4
• Immediate MRI for suspected cauda equina syndrome, severe/progressive neurological deficits, or serious underlying conditions 4

Hip-related pain:

• Anteroposterior pelvis and lateral femoral head-neck radiographs as initial studies 2
• MRI/MRA or CT scan when three-dimensional morphological assessment is indicated 2
• Never diagnose based on imaging alone—combine with symptoms and clinical signs 2

Chest pain:

• 12-lead ECG is standard of care when cause is not clear from history and examination 2
• Biochemical markers (troponins, CK-MB) are recommended as standard tests 2

Laboratory Investigations

• Inflammatory markers: ESR and CRP to assess inflammatory conditions 6
• Complete blood count: Evaluate for infection or malignancy when clinically indicated 4
• Biochemical markers: Troponins for chest pain, alkaline phosphatase for bone pathology 2

Step 4: Pain Subtype Classification

Mechanism-Based Classification

After completing history and examination, classify pain by mechanism to guide treatment:

• Nociceptive somatic: Aching, throbbing, well-localized, responds to NSAIDs and opioids 1
• Nociceptive visceral: Cramping, gnawing, poorly localized, responds to opioids 1
• Neuropathic: Shooting, burning, electric-like, with sensory abnormalities, requires adjuvant analgesics 1, 5
• Mixed: Multiple mechanisms present, requires combination therapy 1

Risk Stratification for Chronicity

Use the STarT Back tool at 2 weeks to identify patients at high risk for chronic disability based on psychosocial factors 4

Common Diagnostic Pitfalls to Avoid

• Over-reliance on pain intensity alone: Intensity does not adequately guide treatment decisions; quality, temporal patterns, and functional impact are equally critical 1, 3
• Premature imaging: Ordering imaging before 4-6 weeks in uncomplicated cases exposes patients to unnecessary radiation without clinical benefit 4
• Ignoring pain descriptors: Failure to assess pain quality prevents identification of neuropathic versus nociceptive mechanisms, which require different pharmacologic strategies 1
• Neglecting psychological factors: Overlooking depression, anxiety, and catastrophizing leaves major treatment targets unaddressed, as these factors often predict disability more strongly than pain intensity 4, 1
• Inadequate neurological examination: Missing sensory abnormalities, allodynia, or hyperalgesia leads to failure in identifying neuropathic pain requiring adjuvant therapy 5
• Failing to document functional interference: Not evaluating how pain interferes with daily activities misses the evaluative dimension that should guide treatment goals 1

Special Population Considerations

• Cognitively impaired or non-verbal patients: Assess pain-related behaviors including facial expression, body movements, vocalizations, interaction changes, and activity alterations rather than relying solely on self-report 1
• Pediatric and elderly patients: These populations are at high risk for inadequate pain management and require adapted assessment approaches 1
• Cultural differences: Consider variations in pain expression across cultures to optimize treatment planning 1