Aids To The Examination Of The Peripheral Nervous System

Clinical Examination of the Peripheral Nervous System: What Actually Matters

Most textbooks will give you a nice checklist. Inspection, palpation, reflexes, sensation, motor testing, autonomic function. That is correct. It is also not particularly useful unless you understand what you are actually looking for and where things go wrong in practice. The peripheral nervous system is far larger and more variable than people give it credit for. A radiculopathy can masquerade as a peripheral neuropathy. A mononeuritis multiplex can look like bilateral distal disease if you are not careful. I spent too long chasing a lumbar radiculopathy in a patient who ultimately had diabetic mononeuropathy because I was following a rigid sequence rather than letting the pattern emerge from the data.

Aids To The Examination Of The Peripheral Nervous System

These aids fall into two categories: clinical techniques and instrumental supports. The clinical side is what you do with your hands and eyes. The instrumental side is what you order when the physical exam is ambiguous or when you need to localize precisely. Both are necessary. Relying on only one gets you in trouble. Start with the inspection. Look at the hands first. Then the feet. Then the face and tongue if there is any reason to suspect cranial nerve involvement. Muscle wasting tells a story before you even touch the patient. Thenar atrophy suggests median nerve pathology at the wrist. Then look for fasciculations, which point toward anterior horn cell disease rather than a peripheral nerve problem. This distinction matters more than people realize. A patient with ALS can have normal reflexes in some limbs and absent ones in others, and the presence of widespread fasciculations should shift your differential immediately. Palpation is about temperature and moisture. Autonomic dysfunction in the peripheral nerves produces cold, dry extremities or sometimes paradoxically sweaty hands. I once missed a small fiber neuropathy in a patient with normal routine nerve conduction studies because I did not check for reduced sweating along the path of the sural nerve. A simple qualitative assessment with a cotton wisp against warm and cool metal surfaces, comparing symmetric sites, caught it. That single observation led to the correct diagnosis instead of another round of unnecessary imaging.

Reflex testing requires a proper hammer and patience. You are not just checking presence or absence. You are looking for the pattern. Hyperreflexia with clonus points centrally. Absent reflexes in a stocking distribution suggest length-dependent polyneuropathy. Asymmetrically absent reflexes suggest a root or plexus issue. I have seen residents dismiss a diminished Achilles reflex as normal variation when it was clearly asymmetric and accompanied by mild weakness. That reflex was the first clue to a S1 radiculopathy that an MRI later confirmed.

Motor Examination Nuances

Motor testing is where most clinicians rush. Do not rush. Test proximal and distal strength separately. Hip flexion, knee extension, ankle dorsiflexion, toe extension, finger abduction, grip. Grade each on the MRC scale from 0 to 5. Document exactly what you find. "Normal" is not a valid finding when you are examining the peripheral nervous system. Write 5/5 or write why you could not assess a particular muscle group. A frequent pitfall is testing against gravity when the patient has true weakness but is compensating with adjacent muscles. Ankle dorsiflexion should be tested with the leg unsupported. Grip strength should be measured after the patient has held their arms out for a few seconds, not immediately upon request. The fatigue component reveals what a single contraction hides.

Sensory Testing Requires Specificity

Light touch with a cotton swab. Pinprick with a fresh neurotip. Vibration with a 128 Hz tuning fork on the bony prominence of the great toe and the medial malleolus. Position sense at the interphalangeal joint of the big toe. These are the four modalities that matter most for peripheral nerve assessment. Temperature testing is useful but difficult to standardize in a busy clinic. Skip it if you are not going to do it consistently. The mapping of sensory loss is critical. Dermatomal patterns point to roots. Stocking-glove patterns point to length-dependent axonal neuropathy. Single nerve territory loss points to entrapment or mononeuropathy. Peroneal nerve palsy at the fibular head produces sensory loss over the lateral calf and dorsum of the foot, not the entire leg. I dealt with a patient who had been referred for lumbar surgery because the sensory map on paper looked dermatomal. The examination showed the sensory loss crossed the midline at the thigh, which is impossible for a single lumbar root. Correct localization avoided unnecessary surgery.

Special Tests Worth Knowing

Tinel sign at the wrist for carpal tunnel syndrome. Phalen maneuver as a confirmatory test. Durkan sign, which is actually more sensitive than both Tinel and Phalen, involves direct compression over the carpal tunnel. I use Durkan exclusively now. The other two generate too many false positives in patients with mild or early disease. Lases test and straight leg raise for radicular irritation. Slump test as a more sensitive alternative for neural tension. Femoral nerve stretch test for upper lumbar roots. These are simple and high yield when positive, though specificity is moderate across the board.

Instrumental Aids

Nerve conduction studies and electromyography remain the cornerstone of instrumental evaluation. NCS distinguishes demyelinating from axonal pathology and localizes the site of lesion. EMG assesses denervation and reinnervation patterns across myotomes and muscles supplied by single nerves. The combination reduces diagnostic uncertainty dramatically, but it is not a substitute for a careful clinical exam. I have seen EMG reports read in isolation lead to incorrect management. A conduction block across a segment may be incidental in an asymptomatic limb. Clinical correlation is mandatory. Quantitative sensory testing measures perceptual thresholds to vibration, heat, and cold. It is useful for small fiber assessment where standard NCS is insensitive. However, it is operator dependent and labor-intensive. I recommend it selectively, not as a screening tool. Routine use in primary care settings produces noise more than signal. Sural nerve and skin biopsy are the gold standard for small fiber neuropathy diagnosis. Reduced intraepidermal nerve fiber density confirms the pathology. This is invasive and should follow a positive QSFT or strong clinical suspicion, not precede it.

Ultrasound of peripheral nerves has matured significantly. Nerve enlargement, flattening at entrapment sites, and abnormal echogenicity are visible. I rely on ultrasound when the clinical picture is unclear and NCS is equivocal. A compressed median nerve at the wrist on ultrasound in the right clinical context is diagnostic without further testing. It also catches structural lesions like ganglion cysts compressing branches of the ulnar nerve, which NCS alone cannot identify.

Practical Limitations and When to Step Back

No examination aid is universal. NCS has a lower limit of detection. Mild axonal loss may produce normal studies. Small fiber neuropathy is invisible to routine electrophysiology. Ultrasound depends entirely on the operator. Clinical patterns can overlap. Diabetic patients frequently have asymptomatic nerve entrapments alongside length-dependent polyneuropathy, and each finding independently may not explain the full symptom picture. If the examination is non-localizing and symptoms are progressive, order imaging of the relevant root or plexus before pursuing invasive testing. If the presentation is classic for a common entrapment neuropathy, treat empirically and reassess in six to eight weeks. Not every peripheral nerve problem needs a full investigative workup immediately. The most useful aid remains a systematic approach combined with honest documentation of what you actually found. Patterns emerge when the data is accurate. They disappear when the data is rushed or interpolated. I have adjusted my entire examination sequence based on patients who presented with atypical features that a rigid textbook approach would have missed. The peripheral nervous system does not care about your checklist.