Lateral Arm Pain With a Sensory Level That Does Not Match the Motor Findings
49-year-old right-handed woman with 6 weeks of right lateral arm and forearm pain, 4/10 at the shoulder and 6/10 radiating toward the thumb and index finger. She denies neck pain. Symptoms are worse after a day at the computer and when lying on the right side. Examination: right biceps and brachioradialis 5/5, right triceps 4+/5, brachioradialis reflex 2+ bilaterally, triceps reflex 1+ on the right and 2+ on the left, pinprick reduced over the right thumb and index finger, right cervical extension-rotation reproduces the arm pain within 10 seconds, right shoulder abduction to 90 degrees eases symptoms within 30 seconds, Phalen's and Tinel's at the wrist negative, shoulder exam unremarkable. Cervical rotation reduced to the right.
1. Localize the lesion and justify your choice, addressing the discordance between the sensory and motor findings.
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What each finding points to
- Motor: triceps 4+/5 -> C7 myotome.
- Reflex: right triceps reflex depressed -> C7 reflex arc.
- Sensory: thumb and index pinprick -> C6 dermatome / median nerve territory.
- Provocation: cervical extension-rotation reproduces the arm pain -> cervical origin, not shoulder or wrist.
- Shoulder abduction relief -> favors a root-level process over a distal entrapment.
Which findings to weight. Objective motor and reflex findings are far more reliable localizers than the patient's perception of where tingling is felt. Dermatomal self-localization is notoriously imprecise, and adjacent root territories interdigitate; tingling in a median-nerve distribution can accompany a C7 lesion. My working localization is therefore a right C7 radiculopathy, most likely at C6-7, with the sensory complaint treated as the outlier that requires explanation rather than as the anchor.
The reasoning trap to avoid is anchoring on 'thumb and index means C6' and then explaining away the triceps weakness and reflex loss. The objective signs are the anchor; the subjective symptom is the variable. If the picture were reversed -- objective C6 findings with C7-distributed tingling -- the localization would likewise follow the objective data.
2. What alternative diagnoses would you consider, and which specific findings would change your mind?
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- Carpal tunnel syndrome. Produces median-distributed symptoms without reflex change or triceps weakness. Her Phalen's and Tinel's are negative, and the shoulder abduction relief sign is not a carpal tunnel phenomenon. It would become more likely with ring-finger sensory splitting, thenar atrophy, nocturnal-only symptoms, and a normal cervical and reflex exam.
- Cervical spondylotic myelopathy. Look for hyperreflexia, clonus, Hoffmann's, Babinski, spasticity, or a sensory level. None present, but this is the diagnosis that must never be missed in a cervical case.
- Brachial plexopathy or Pancoast tumor. A plexopathy usually crosses myotomes, has a more explosive painful onset, and may show scapular winging. A Pancoast lesion should be considered with any C8-T1 pattern, Horner's syndrome, or a smoking history.
- Rotator cuff or subacromial pathology. The shoulder exam is unremarkable and abduction relieves rather than provokes, which argues against it.
Change-my-mind triggers: progressive motor loss, new sensory level, bilateral symptoms, bowel or bladder change, upper motor neuron signs, or failure to improve over 6-8 weeks. Those triggers convert a clinical diagnosis into an imaging-and-electrodiagnostic one. EMG/NCS is also useful when the level is genuinely ambiguous, since it can separate radiculopathy from entrapment and quantify axonal loss.
3. How would you manage her for the first six weeks, and what would trigger imaging or referral?
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Weeks 0-6: no imaging is required for a clinically stable radiculopathy whose level matches the examination. Imaging at this stage mostly produces findings that must then be explained away.
- Activity modification rather than bed rest; keep working with positional breaks.
- Cervical mobilization and intermittent traction within a comfortable range; thoracic and scapular mobility work.
- Isometric cervical strengthening and scapular retraction, progressed as tolerated.
- Analgesia coordinated with her primary care physician rather than self-selected.
- Re-evaluate at 2 weeks on trajectory (function, sleep, work tolerance), not on pain score alone.
Order MRI or refer when: triceps strength drops below 4/5 or any motor deficit progresses; symptoms persist beyond 6-8 weeks without meaningful change; the level becomes uncertain; or any myelopathic or upper motor neuron sign appears. Same-day urgent referral and MRI for bowel or bladder change, bilateral lower extremity involvement, saddle symptoms, or rapidly progressive weakness.
Documentation point: the baseline neuro exam recorded today -- specific myotome grades and reflex comparisons -- is what makes the 2-week comparison meaningful. 'Neuro intact' is not a baseline.