What is the differential diagnosis and management approach for an adult patient with radiculopathy, possibly presenting with a history of back pain or recent trauma?

Differential Diagnosis for Radiculopathy

Primary Differential Considerations

The differential diagnosis for radiculopathy must first distinguish true nerve root compression from plexopathy, peripheral nerve entrapment, and referred somatic pain, as these conditions present with overlapping symptoms but require fundamentally different management approaches. 1, 2

Mechanical Nerve Root Compression (True Radiculopathy)

• Herniated disc with nerve root impingement is the most common cause, presenting with dermatomal pain, sensory loss, and motor weakness in a specific nerve root distribution 1, 3
• Cervical or lumbar spondylosis with foraminal stenosis from osteophytes or facet arthropathy causes progressive radicular symptoms 1, 3
• Spinal stenosis produces multilevel radiculopathy, particularly in the lumbar spine, with neurogenic claudication 1
• Ossification of posterior longitudinal ligament (OPLL) causes progressive myelopathy and radiculopathy, particularly in the thoracic spine 1

Plexopathy (Not Radiculopathy)

• Brachial plexopathy presents with pain and weakness in multiple peripheral nerve distributions (not single dermatomal), distinguishing it from cervical radiculopathy 1
• Lumbosacral plexopathy causes symptoms in multiple nerve territories (L1-S4), not confined to single nerve root distribution 1
• Key distinguishing feature: Plexopathy affects multiple peripheral nerves simultaneously, while radiculopathy follows a single dermatomal pattern 1

Peripheral Nerve Entrapment Syndromes

• Carpal tunnel syndrome mimics C6-C7 radiculopathy but lacks neck pain and has positive Phalen's/Tinel's signs 2
• Ulnar neuropathy at the elbow can mimic C8-T1 radiculopathy but spares the medial forearm 2
• Thoracic outlet syndrome presents with vascular or neurogenic symptoms during arm elevation, not with positive Spurling's test 3, 2
• Peroneal nerve entrapment mimics L5 radiculopathy but lacks back pain and has localized tenderness at fibular head 2

Somatic Referred Pain (Non-Radicular)

• Facet joint arthropathy causes localized mechanical pain that may radiate to trapezius or buttock but lacks dermatomal distribution 3, 4
• Myofascial pain syndrome presents with trigger points and referred pain patterns that do not follow dermatomal maps 5
• Sacroiliac joint dysfunction mimics L5-S1 radiculopathy but lacks true neurologic deficits 5

Critical "Red Flag" Conditions Requiring Urgent Evaluation

Infectious Etiologies

• Vertebral osteomyelitis or discitis presents with fever, elevated ESR/CRP, and history of IV drug use or immunosuppression 3, 6
• Epidural abscess causes progressive neurologic deficits with constitutional symptoms and requires emergency MRI 1

Neoplastic Etiologies

• Metastatic disease to spine presents with intractable pain, constitutional symptoms (weight loss, night sweats), and history of malignancy 1, 3
• Primary spinal tumors cause progressive symptoms refractory to conservative treatment 3
• Leptomeningeal carcinomatosis requires MRI with contrast for detection 1

Inflammatory/Autoimmune Conditions

• Inflammatory arthritis (ankylosing spondylitis, rheumatoid arthritis) causes persistent pain with elevated inflammatory markers 3, 6
• Neuralgic amyotrophy (Parsonage-Turner syndrome) presents with acute severe shoulder pain followed by weakness, mimicking cervical radiculopathy 2

Compressive Myelopathy

• Cervical or thoracic myelopathy requires differentiation from radiculopathy through examination for hyperreflexia, Babinski sign, gait disturbance, and bowel/bladder dysfunction 1
• Cauda equina syndrome presents with bilateral leg symptoms, saddle anesthesia, and bowel/bladder dysfunction requiring emergency surgery 1

Diagnostic Algorithm

Step 1: Screen for Red Flags

Immediately obtain MRI if ANY of the following are present: 1, 3

• Constitutional symptoms (fever, unexplained weight loss, night sweats)
• Elevated inflammatory markers (ESR, CRP, WBC)
• History of malignancy or immunosuppression
• IV drug use
• Progressive or severe neurologic deficits
• Intractable pain despite appropriate conservative therapy
• Vertebral body tenderness on palpation
• Bowel/bladder dysfunction

Step 2: Distinguish Radiculopathy from Mimics

Perform focused neurologic examination: 3, 2

• Spurling's test: Highly specific for cervical radiculopathy when positive (neck extension with lateral rotation and axial compression reproduces arm pain) 3
• Straight leg raise: Positive if reproduces leg pain below knee at <60 degrees elevation, indicating lumbar radiculopathy 1
• Dermatomal sensory testing: True radiculopathy follows specific dermatomal patterns, though variant innervation occurs in 10-15% of cases 7
• Myotomal motor testing: Weakness in specific myotomes (C5=deltoid, C6=biceps/wrist extensors, C7=triceps, C8=finger flexors, L4=quadriceps, L5=ankle dorsiflexors, S1=ankle plantarflexors) 8
• Reflex testing: Diminished reflexes in radiculopathy (biceps=C5-C6, triceps=C7, knee=L4, ankle=S1) 8

Key distinguishing features: 1, 2, 5

• Radiculopathy: Dermatomal pain/sensory loss + myotomal weakness + diminished reflex in single nerve root distribution
• Plexopathy: Multiple peripheral nerve territories affected simultaneously, not single dermatomal
• Peripheral entrapment: Localized tenderness, positive provocative tests (Tinel's, Phalen's), spares proximal muscles
• Somatic referred pain: No true neurologic deficits (normal strength, sensation, reflexes), mechanical pain pattern

Step 3: Imaging Strategy Based on Clinical Presentation

For acute symptoms (<6 weeks) WITHOUT red flags: 1

• No imaging initially—75-90% of cervical radiculopathy and most lumbar radiculopathy resolve with conservative management 4
• Reassess at 6-8 weeks; if persistent symptoms, proceed to MRI

For chronic symptoms (>6-8 weeks) or consideration for intervention: 1

• MRI without contrast is the preferred initial imaging modality for evaluating soft tissue abnormalities, disc herniation, nerve root impingement, and spinal canal stenosis 1
• MRI with contrast is indicated when infection, tumor, or inflammatory process is suspected 1

For patients with contraindications to MRI: 1

• CT myelography provides excellent visualization of nerve root compression and spinal canal stenosis 1

Plain radiographs have limited utility: 1

• May serve as initial screen for gross spondylosis or malalignment, but degenerative changes correlate poorly with symptoms (present in 85% of asymptomatic individuals over 30) 3

Step 4: Consider Electrodiagnostic Testing

EMG/nerve conduction studies are NOT routinely necessary but should be considered when: 3, 8

• Diagnosis remains unclear after clinical evaluation and MRI
• Need to differentiate between radiculopathy and peripheral nerve entrapment
• Multiple levels of pathology on imaging require localization of symptomatic level
• Medicolegal documentation required

Critical Pitfalls to Avoid

Imaging Interpretation Errors

• Do not assume degenerative changes on imaging are causative without clinical correlation—spondylotic changes are present in 85% of asymptomatic individuals over 30 years 3
• Bulging disc without nerve root impingement is a nonspecific finding and does not explain radicular symptoms 1
• Variant nerve root innervation occurs in 10-15% of cases, causing clinical-imaging mismatch where symptoms suggest adjacent level pathology 7

Clinical Assessment Errors

• Do not miss myelopathy masquerading as radiculopathy—always test for hyperreflexia, Babinski sign, and gait disturbance 1
• Do not diagnose thoracic outlet syndrome when radiculopathy is present—TOS has vascular symptoms with arm elevation, not positive Spurling's test 3, 2
• Do not overlook "double crush" phenomenon—patients can have both radiculopathy and peripheral entrapment simultaneously 2

Management Errors

• Do not order immediate imaging for acute radiculopathy without red flags—this leads to overdiagnosis of incidental findings and unnecessary interventions 3
• Do not delay imaging when red flags are present—infection, tumor, and cauda equina syndrome require urgent diagnosis and treatment to prevent permanent neurologic injury 1, 3

Quantitative Sensory Testing Findings

Patients with true radiculopathy demonstrate: 5

• More pronounced loss of small-fiber function
• Increased mechanical hyperalgesia (lower pressure pain threshold)
• Loss of mechanical detection (higher mechanical detection threshold)
• Higher PainDETECT scores (>14 suggests neuropathic component)
• The combination of pressure pain threshold, mechanical detection threshold, numbness, and prickling provides best predictive value for detecting radiculopathy 5