Right arm pain in a carpenter: which root, and does he need imaging today?
A 47-year-old carpenter reports 6 weeks of right neck and shoulder pain that now shoots into the right thumb and index finger. He has no fever, no trauma, no night pain, and no bowel or bladder change. Examination: right biceps reflex 1+, right brachioradialis 1+, right triceps 2+, left arm reflexes 2+ and symmetric. Manual muscle testing shows right elbow flexion 4/5, right wrist extension 4/5, right triceps 5/5, deltoid 5/5, and grip 5/5. Spurling maneuver on the right reproduces the arm pain at 30 degrees of extension. Sensation is diminished over the right thumb. Cervical extension is limited and painful. He asks two things: does he need an MRI today, and can he keep working?
1. Localize the lesion to a specific nerve root and disc level, and justify the answer using dermatome, myotome, and reflex findings.
Read the worked answer
C6 nerve root, C5–C6 disc level.
- Dermatome: thumb and index finger = C6. C7 would be the middle finger; C5 the lateral shoulder/upper arm.
- Myotome: wrist extension (ECRL/ECRB) is the C6 key muscle at 4/5. Elbow flexion (biceps/brachialis, C5–C6) also 4/5.
- Reflex: brachioradialis (C6) and biceps (C5–C6) both depressed to 1+ on the symptomatic side.
- Spared structures argue against neighbors: deltoid (C5, axillary nerve) and triceps (C7, radial nerve) are 5/5 with a 2+ triceps reflex.
- Anatomy of the level: C1–C7 roots exit above their same-numbered pedicle, so a posterolateral disc at C5–C6 compresses the C6 root in that foramen. The disc level is therefore one segment above the root number - a very common source of mislabeling on exam questions.
2. Explain why the deltoid and triceps are spared, and state what examination findings would instead have pointed to a C5 or C7 root.
Read the worked answer
Why they are spared: the herniation is compressing one root within one foramen. The deltoid is C5 (axillary nerve); the triceps and triceps reflex are C7 (radial nerve). Neither root is compressed by a C5–C6 paramedian disc.
If it were C5: deltoid and supraspinatus/infraspinatus weakness, biceps reflex depression, sensory loss over the lateral shoulder, and pain referred to the shoulder rather than the thumb.
If it were C7: triceps weakness and a depressed triceps reflex, wrist flexion weakness, sensory loss over the middle finger, and a C6–C7 disc on imaging.
This pattern-recognition step matters because the level drives both the injection/surgical target and the prognosis for the expected time course.
3. He asks about MRI today and about continuing to work. Justify a management decision using the red-flag framework, and state the triggers that would change it.
Read the worked answer
No red flags are present, so immediate MRI is not required.
Red flags that would justify urgent imaging/referral:
- Myelopathy: gait disturbance, clumsy hands, lower-extremity hyperreflexia or Babinski, bowel/bladder dysfunction, Lhermitte sign. (The case describes none - but the lower limbs and gait should be examined explicitly, because a normal upper-limb reflex on the left does not exclude cord compression.)
- Progressive or severe motor deficit (≤3/5), especially if worsening across visits.
- Infection or malignancy risk: fever, IV drug use, immunosuppression, cancer history, unexplained weight loss, night pain unrelieved by rest.
- Trauma or suspected fracture/instability.
Work: he may continue with modified duty - avoid sustained cervical extension, overhead work, and heavy load carriage. Reassess in 4–6 weeks. Obtain MRI sooner if a red flag appears or weakness progresses; obtain MRI/EMG if symptoms persist beyond 6–8 weeks or if surgery is being considered. A 4/5 wrist extensor with intact triceps and no cord signs is compatible with a favorable natural history.