Clinical neurophysiology Study Guide

📖 Core Concepts Clinical Neurophysiology – Study of the CNS and PNS by recording spontaneous or stimulated bio‑electrical activity. Electrodiagnostic Medicine – Sub‑field focusing only on the peripheral nervous system (NCS, needle EMG, evoked potentials). Diagnostic Purpose – Pinpoint the site, type, and severity of a nervous‑system lesion; primarily a diagnostic, not therapeutic, tool. Key Modalities Electromyography (EMG) & Nerve Conduction Studies (NCS) – Measure muscle electrical activity and signal speed along peripheral nerves. Electroencephalography (EEG) – Records thalamocortical brain rhythms from scalp electrodes; essential for seizure evaluation. Evoked Potentials (EP) – Brain/spinal‑cord responses to visual, auditory, or somatosensory stimulation; test specific neural tracts. Polysomnography – Full‑night sleep study for abnormal sleep‑behavior disorders. Intra‑operative Neurophysiologic Monitoring (IONM) – Real‑time functional recording during surgery to protect neural structures. 📌 Must Remember Clinical neurophysiology ≠ treatment – it defines lesions, doesn’t cure them. Electrodiagnostic medicine = peripheral‑only (NCS, needle EMG, EP). EEG → seizures & CNS abnormalities; EMG/NCS → muscle, nerve, root disorders. Evoked potentials are modality‑specific: visual (VEP), auditory (BAEP), somatosensory (SSEP). Polysomnography = sleep architecture + respiratory & leg‑movement monitoring. IONM is only used intra‑operatively to give immediate feedback to the surgical team. 🔄 Key Processes Nerve Conduction Study (NCS) Workflow Place surface electrodes over a peripheral nerve. Deliver a brief supra‑threshold stimulus proximally. Record latency, amplitude, and conduction velocity distally. Needle EMG Procedure Insert fine‑wire needle into target muscle. Record spontaneous activity (fibrillation, positive sharp waves). Assess motor unit action potential size, shape, recruitment pattern. EEG Recording Apply 10‑20 system scalp electrodes. Capture continuous electrical activity; analyze frequency bands (delta‑theta‑alpha‑beta‑gamma). Evoked Potential Testing Stimulate specific sense (e.g., flash for VEP). Average multiple responses to extract the low‑amplitude cortical wave. Polysomnography Setup Attach EEG, EOG, EMG (chin & legs), respiratory effort belts, pulse oximetry. Record overnight; stage sleep and identify apneas/hypopneas. 🔍 Key Comparisons Clinical Neurophysiology vs. Electrodiagnostic Medicine Scope: Whole CNS & PNS vs. peripheral‑only. Techniques: EEG, polysomnography, IONM added vs. NCS/EMG/EP only. EEG vs. EMG/NCS Target: Brain cortical activity vs. muscle/nerve peripheral activity. Primary Use: Seizure/brain disorders vs. neuromuscular diseases. Evoked Potentials vs. Routine EEG Stimulus: Specific sensory input (visual, auditory, somatosensory) vs. resting spontaneous activity. Goal: Test integrity of defined pathways vs. overall cortical rhythm assessment. ⚠️ Common Misunderstandings “Neurophysiology treats disease.” – It only diagnoses and localizes lesions. All EEG findings are epileptic. – Many patterns (e.g., benign rhythmic activity) are normal or nonspecific. NCS measures muscle strength. – It measures conduction speed/amplitude, not force. Polysomnography is just an overnight EEG. – It also records breathing, oxygenation, and limb movements. 🧠 Mental Models / Intuition “Road map” model: Think of each modality as a map of a different “road” in the nervous system—EEG = highways (cortex), NCS = local streets (peripheral nerves), EP = bridges (specific sensory tracts). Signal‑to‑noise averaging: Evoked potentials are tiny; averaging many trials is like stacking multiple blurry photos to get a clear picture. 🚩 Exceptions & Edge Cases NCS in very distal nerves may show prolonged latency due to limb length, not pathology. EEG during sleep can display patterns (e.g., sleep spindles) that mimic focal slowing; interpret in clinical context. Polysomnography may be normal in patients with daytime sleepiness caused by circadian rhythm disorders (not captured by the study). 📍 When to Use Which Suspected seizure → Order EEG first. Peripheral neuropathy or radiculopathy → NCS + Needle EMG. Demyelinating optic pathway disease → Visual evoked potentials (VEP). Unexplained sleep‑related complaints → Polysomnography. High‑risk spine or brain surgery → Intra‑operative neurophysiologic monitoring. 👀 Patterns to Recognize Slowed conduction velocity + reduced amplitude → Demyelinating vs. axonal loss. Diffuse generalized slowing on EEG → Metabolic encephalopathy. Absent or delayed EP waveforms → Lesion in the corresponding sensory tract. Periodic limb movements on polysomnography → Restless legs syndrome or sleep‑related movement disorder. 🗂️ Exam Traps Choosing “EEG” for a peripheral nerve problem – distractor; correct answer is NCS/EMG. Assuming all evoked potentials are performed intra‑operatively – many are outpatient diagnostic tests. Confusing “electrodiagnostic medicine” with “clinical neurophysiology” – remember the former is peripheral‑only. Selecting polysomnography for diagnosing insomnia – sleep study evaluates breathing & movement disorders, not primary insomnia. --- Focus on these high‑yield points when you review; they map directly to the core exam concepts in clinical neurophysiology.