7.2 Clinical Impression from Physical and NMS Exam
Key Takeaways
- Every physical/NMS finding maps to one of five mechanisms: radiculopathy, peripheral nerve entrapment, joint mechanical dysfunction, myofascial/soft tissue, or visceral referral/vascular
- Spinal nerve root level is localized by converging myotome, dermatome, and reflex findings, not any single test alone
- Upper motor neuron signs (hyperreflexia, clonus, positive Babinski/Hoffmann) indicate myelopathy and must not be mistaken for a simple radiculopathy pattern
- Orthopedic test clusters (SLR plus crossed SLR, Kemp's plus flexion-distraction relief, Spurling's plus distraction relief) raise diagnostic confidence far more than an isolated positive test
- 5 D's and 3 N's on cervical motion testing, absent perianal sensation, and hyperreflexia with clonus are exam findings that mandate immediate referral rather than continued differential-building
Section 7.1 built a working differential from the case history alone. Section 7.2 is where that differential gets tested against objective findings -- and Part III rewards candidates who can explain why a finding implicates a mechanism, not just recall that a test is positive. Every physical and neuromusculoskeletal (NMS) finding on the exam maps back to one of five broad pathophysiologic mechanisms, and matching finding to mechanism is the core skill in this section.
Five Mechanisms Behind Every NMS Finding
| Mechanism | What Is Compressed/Irritated | Signature Findings |
|---|---|---|
| Radiculopathy (nerve root) | Spinal nerve root at or near the foramen | Dermatomal sensory loss, myotomal weakness, diminished specific reflex, positive nerve tension sign |
| Peripheral nerve entrapment | Named peripheral nerve at a fixed anatomic tunnel | Findings follow peripheral nerve distribution, not dermatome; provocative test reproduces symptoms at the entrapment site |
| Joint mechanical dysfunction | Facet, SI joint, or peripheral joint capsule | Pain reproduced with joint loading/compression, restricted or aberrant motion, no neuro deficit |
| Myofascial/soft tissue | Muscle, tendon, fascia | Pain with resisted contraction or stretch, palpable taut band or trigger point, normal neuro and joint tests |
| Visceral referral or vascular | Organ system or vessel referring pain to the musculoskeletal frame | Pain pattern does not fit a dermatome or myotome; associated systemic or organ-specific signs (fever, pulsatile mass, bowel change) |
Reading a Part III exam vignette is largely an exercise in elimination across this table: does the finding follow a dermatome (radiculopathy), a named peripheral nerve (entrapment), a joint-loading pattern (mechanical), a contractile pattern (myofascial), or none of the above (visceral/vascular)?
Neurological Exam: Reading the Level
When the mechanism is radicular, the exam should localize a spinal level using three converging data points -- myotome (motor), dermatome (sensory), and reflex:
| Nerve Root | Myotome (Weak Motion) | Dermatome | Reflex |
|---|---|---|---|
| C5 | Shoulder abduction | Lateral arm | Biceps |
| C6 | Elbow flexion, wrist extension | Thumb | Brachioradialis |
| C7 | Elbow extension, wrist flexion | Middle finger | Triceps |
| L4 | Knee extension | Medial leg/ankle | Patellar |
| L5 | Great toe/foot dorsiflexion | Dorsum of foot, great toe | None reliable (medial hamstring) |
| S1 | Ankle plantarflexion | Lateral foot | Achilles |
A single finding is weak evidence; three findings converging on the same level (for example, weak great toe extension plus numb dorsal foot plus normal reflexes, since L5 has no dependable reflex) is strong evidence for that specific root.
Upper vs. Lower Motor Neuron: Don't Confuse Radiculopathy with Myelopathy
A frequently tested distinction is radiculopathy (lower motor neuron, nerve root) versus myelopathy (upper motor neuron, spinal cord):
- Lower motor neuron (radiculopathy): Diminished or absent reflex, flaccid weakness, focal dermatomal sensory loss, negative pathological reflexes.
- Upper motor neuron (myelopathy): Hyperreflexia, spasticity, positive Babinski/Hoffmann sign, clonus, gait disturbance, bilateral or diffuse presentation rather than a single root.
Mistaking a myelopathy pattern for a simple radiculopathy is a classic Part III distractor -- hyperreflexia and a positive Babinski sign in a patient with neck pain should immediately raise cervical myelopathy, not cervical radiculopathy, and this distinction changes both urgency and next steps.
Orthopedic Test Clusters Beat Single Tests
Individual orthopedic tests have limited sensitivity or specificity in isolation; Part III vignettes are written around clusters that raise diagnostic confidence:
- Straight leg raise (SLR) positive between 30-70 degrees plus crossed SLR positive -- high specificity for lumbar disc herniation with nerve root involvement.
- Kemp's test reproduces pain plus relief with flexion/distraction -- facet-mediated or foraminal encroachment pattern rather than pure disc pathology.
- Spurling's test positive plus relief with cervical distraction -- cervical foraminal nerve root compression.
- Positive Tinel's and Phalen's at the wrist, normal cervical exam -- localizes to carpal tunnel (median nerve entrapment), not a cervical root.
- Adson's test positive with radial pulse diminution on arm positioning -- thoracic outlet syndrome, a vascular/neurogenic entrapment distinct from a cervical radiculopathy.
When the Exam Itself Is the Red Flag
Some exam findings stop the workup and mandate immediate referral rather than continued differential building:
- 5 D's (dizziness, diplopia, dysarthria, dysphagia, drop attacks) and 3 N's (nausea, nystagmus, numbness) on cervical motion testing -- suspected vertebrobasilar insufficiency (VBI); stop provocative testing and refer.
- Absent perianal sensation, decreased rectal tone -- cauda equina confirmation; emergency referral.
- Hyperreflexia with clonus and a positive Babinski -- myelopathy; urgent referral for imaging.
Worked Example
A 52-year-old presents with lateral leg and dorsal foot numbness. Exam reveals weak great toe extension, intact Achilles reflex, negative straight leg raise but positive crossed SLR at 60 degrees, and no long-tract signs. The mechanism is radicular (dermatomal/myotomal pattern with a positive nerve tension sign), the level is L5 (myotome and dermatome converge, and the absence of a reliable L5 reflex is expected, not reassuring against the diagnosis), and the crossed SLR finding raises confidence that a disc herniation -- not a peripheral entrapment or myofascial cause -- is compressing the L5 root.
Exam Tip
When a Part III EMCQ case adds exam findings to an already-built history differential, your job is to eliminate categories, not just confirm the leading hypothesis. If the history suggested mechanical low back pain but the exam reveals hyperreflexia and clonus, the correct clinical impression pivots to myelopathy -- the exam finding outranks the history-based pretest probability.
A patient has pain and numbness that follow the exact distribution of the median nerve at the wrist, with a normal cervical exam and no dermatomal pattern above the wrist. Which mechanism best explains this presentation?
A patient with neck pain also demonstrates hyperreflexia, a positive Hoffmann sign, and mild gait disturbance. These upper motor neuron findings should shift the clinical impression from cervical radiculopathy to which diagnosis?
A positive straight leg raise at 45 degrees combined with a positive crossed straight leg raise most strongly supports which diagnosis?