What is the diagnosis and management for a middle-aged to elderly patient with long-term arm pain and numbness, who later develops right leg numbness and weakness towards the groin?

Diagnosis: Multilevel Radiculopathy or Lumbosacral Plexopathy

This patient's presentation of long-term arm pain and numbness followed by right leg numbness and weakness toward the groin suggests multilevel radiculopathy affecting both cervical and lumbosacral nerve roots, or alternatively, a progressive plexopathy affecting multiple nerve distributions. 1, 2

Critical Diagnostic Considerations

Pattern Recognition for Localization

The sequential involvement of upper extremity followed by lower extremity points toward:

• Cervical radiculopathy (C5-T1) causing the arm symptoms, with pain radiating in dermatomal distribution accompanied by sensory loss or motor weakness 1, 3
• Lumbar radiculopathy (L3-L4) causing groin-region symptoms, as L3 radiculopathy characteristically produces symptoms at the upper buttock and ventral surface of the thighs, while L4 affects the ventro-lateral surfaces of the thigh and leg 4
• Lumbosacral plexopathy as an alternative diagnosis, particularly if symptoms don't follow strict dermatomal patterns and involve multiple nerve distributions simultaneously 1, 2

Key Historical Features to Elicit

• Onset pattern and tempo: Acute onset suggests traumatic or inflammatory causes (Guillain-Barré syndrome, chronic inflammatory demyelinating polyneuropathy), while insidious progression over months to years suggests structural compression, chronic inflammatory processes, or infiltrative lesions 5, 2, 6
• Pain characteristics: Sharp, lancinating pain radiating down the limb suggests radiculopathy, while burning or electric sensations in multiple peripheral nerve distributions suggest plexopathy 1
• Positional factors: Symptoms worsening with neck extension or sitting suggest cervical radiculopathy or spinal stenosis, while relief with position changes points toward mechanical compression 1, 7
• Preceding events: Recent infections, vaccinations, or trauma may trigger inflammatory neuropathies 8

Essential Physical Examination Findings

Upper Extremity Assessment:

• Identify specific muscle weakness patterns to localize cervical nerve root involvement (C5-T1) 1, 3
• Map sensory distribution to determine if symptoms follow dermatomal patterns versus peripheral nerve distributions 3
• Assess deep tendon reflexes (biceps C5-C6, triceps C7, brachioradialis C6) for asymmetry or absence 1

Lower Extremity Assessment:

• Test hip flexion (L2-L3), knee extension (L3-L4), ankle dorsiflexion (L4-L5), and plantar flexion (S1) to localize lumbar root involvement 4, 2
• Examine sensory distribution: L3 affects ventral thigh and knee; L4 affects lateral shin; L5 affects lateral leg; S1 affects lateral calf and foot 4
• Assess patellar (L3-L4) and ankle (S1) reflexes for asymmetry or absence 2, 6
• Palpate femoral, popliteal, dorsalis pedis, and posterior tibial pulses to exclude vascular claudication 1

Red Flag Assessment:

• Bilateral motor weakness, saddle anesthesia, urinary retention, or new bowel/bladder dysfunction indicate cauda equina syndrome requiring emergency surgical referral 7

Diagnostic Workup Algorithm

First-Line Investigations

Electrodiagnostic Studies (NCS/EMG):

• Perform nerve conduction studies and electromyography to differentiate radiculopathy from plexopathy from peripheral neuropathy 1, 2, 6
• Radiculopathy shows denervation in paraspinal muscles with myotomal distribution of abnormalities 1
• Plexopathy shows abnormalities in multiple nerves from the same plexus without paraspinal involvement 1, 2
• Chronic inflammatory demyelinating polyneuropathy shows partial conduction blocks with nonuniform slowing 6

MRI Imaging:

• Obtain MRI of the cervical spine to evaluate for disc herniation, foraminal stenosis, or spinal cord compression causing arm symptoms 1
• Obtain MRI of the lumbosacral spine to evaluate for disc herniation, spinal stenosis, or nerve root compression causing leg symptoms 1, 7
• If electrodiagnostic studies suggest plexopathy, obtain dedicated MRI of the brachial plexus and lumbosacral plexus to identify nerve enlargement, T2 signal abnormality, or masses 1, 2

Second-Line Investigations (If Initial Workup Non-Diagnostic)

Cerebrospinal Fluid Analysis:

• Obtain if inflammatory neuropathy (chronic inflammatory demyelinating polyneuropathy) is suspected, looking for albuminocytologic dissociation (elevated protein >45 mg/dL with normal cell count <5 cells/μL) 9, 8, 6

Laboratory Testing:

• Serum ferritin if restless legs syndrome is considered (values <50 ng/mL suggest iron deficiency) 1
• Hemoglobin A1c and fasting glucose to assess for diabetic neuropathy 9
• Vitamin B12, folate, thyroid function tests to exclude metabolic neuropathies 8

Management Strategy

Conservative Management for Confirmed Radiculopathy

• Maintain physical activity with postural modifications to avoid positions that exacerbate symptoms 7
• Prescribe acetaminophen or NSAIDs for pain control 1, 7
• Refer to physical therapy for stretching and strengthening exercises, which have demonstrated effectiveness for managing musculoskeletal symptoms 1
• Consider acupuncture as complementary therapy, which has shown efficacy in decreasing pain intensity in multiple trials 1

Specialist Referral Indications

Immediate Neurosurgical Referral:

• Bilateral motor weakness, saddle anesthesia, urinary retention, or new bowel/bladder dysfunction (cauda equina syndrome) 7
• Progressive motor weakness despite conservative management 7

Neurology Referral:

• Suspected plexopathy based on electrodiagnostic findings or clinical pattern not matching radiculopathy 1, 2
• Suspected chronic inflammatory demyelinating polyneuropathy, which requires immunotherapy with intravenous immunoglobulin or plasma exchange 9, 6
• Electrodiagnostic findings of demyelinating polyneuropathy with partial conduction blocks 6

Common Pitfalls to Avoid

• Do not assume all leg numbness is lumbar radiculopathy—groin numbness specifically suggests L3 involvement or upper lumbar plexopathy, not the more common L5-S1 radiculopathy 4
• Do not miss bilateral symptoms or progressive weakness, which may indicate serious conditions like chronic inflammatory demyelinating polyneuropathy requiring urgent treatment 9, 6
• Do not delay MRI if red flag symptoms are present, as cauda equina syndrome requires surgical decompression within 48 hours to prevent permanent neurological deficit 7
• Do not attribute all symptoms to peripheral arterial disease without checking pulses and ankle-brachial index, as neurogenic and vascular claudication have distinct relief patterns 1, 7