So, I am- ... um, MBBS student in India, and, um- Mm-hmm ... basically, medicine is what I sometimes fear a lot because there is so much of knowledge to gain from it. And- Mm-hmm ... I kind of love the subject, but, you know, the teachers make it seem very difficult or, you know, they are so strict that it just burns me out to study it. Anyways, the main thing in this is theory anyways I can do from the Meru videos and lectures, prep letter videos, and, you know, the textbooks and stuff. I get knowledge from the-- those textbooks, and they are pretty easy if you go to see, if you go to learn the concepts and all. It is kind of easy, but when it comes to the clinics where you have to come to a diag- diagnosis, give differentials of the di- di- differentials of the patient, differential diagnosis for the patient, I go blank. Like, how to go about a case? Like, for example, if we talk about cardiology, there are so many things that a person can come with, even if it is just a chest pain. Like, there are so many things. So, how do we go about, um, symptoms to come to a particular diagnosis or to give differentials of the diagnosis? How to think about-- How to think like a doctor? Like, you know, how to rule out stuff in the history that you come to differentials of that particular patients? And, um, so we can-- Can we start with, uh, cardiology section? Because that is the one which I find kind of difficult because the murmurs, the things, and all. So, referring to Harrison's textbook, um, we can just go in a very, uh, stepwise manner of each chief complaint in cardiology and how to go about it, uh, in a case, like what things to look for and what things to rule out in each system for cardiology to come to a diagnosis that this is the case of cardiology and not RS. This is the case of cardiology, and it doesn't have any CNF manifestation. This is a case of cardiology. It is not related to abdomen. So how to rule out those things?

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Great question - and honestly, the "going blank" feeling in clinics is one of the most common experiences for MBBS students. The fix is learning a structured clinical reasoning framework, not memorizing more facts. Let me build this out for you from Harrison's, starting with cardiology.

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I now have excellent, rich content from Goldman-Cecil Medicine. Let me get a few more key sections - the syncope/murmur approach and the Harrison's-specific framework.

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I now have everything I need to build a thorough, well-structured guide. Let me compose the full answer.

How to Think Like a Doctor in Cardiology: A Clinical Reasoning Framework for MBBS Students

First, understand this: going blank in the clinic is NOT a knowledge problem - it's a framework problem. You have the facts. What you're missing is a mental scaffold to hang them on. Once you have that scaffold, the facts slot in automatically.

The Core Principle: Problem Representation

Before you can give differentials, you need to convert what the patient says into a "problem representation" - a one-liner that captures who the patient is, what the chief complaint is, and its key features.

"A 55-year-old hypertensive male presenting with sudden onset central chest pain radiating to the left arm, associated with sweating, lasting 30 minutes, not relieved by rest."

This one sentence already narrows your differentials dramatically. Practice building this sentence for every patient before you open your mouth in clinic.

Step 1: The 7 Cardinal Symptoms of Cardiology

According to Goldman-Cecil Medicine, the cardinal symptoms of cardiovascular disease are:

Chest pain or discomfort
Dyspnea (breathlessness)
Palpitations
Syncope / pre-syncope / lightheadedness
Edema
Fatigue
Cough / hemoptysis (when cardiac in origin)

Every cardiology case will present with one or more of these. Your job is to characterize each symptom completely.

Step 2: The SOCRATES Framework for Characterizing Symptoms

For every symptom the patient reports, ask:

Letter	Stands for	Why it matters in Cardiology
S	Site	Central = cardiac/aortic; Lateral = pleuritic/PE
O	Onset	Sudden = dissection/PE/arrhythmia; Gradual = HF/angina
C	Character	Crushing/pressure = ischemia; Tearing = dissection; Sharp = pericarditis/MSK
R	Radiation	Left arm/jaw = MI; Back = dissection; Shoulder tip = pericarditis
A	Associated Sx	Sweating/nausea = MI; Hemoptysis = PE; Orthopnea/PND = HF
T	Time/Duration	>30 min = MI; <20 min with rest-relief = stable angina
E	Exacerbating/Relieving	Exertion-worsened = angina/AS; Position-worsened = pericarditis
S	Severity	Severity + progression pattern

Step 3: Cardiology Chief Complaint by Chief Complaint

CHEST PAIN - The Big Differentials

Here is the key teaching from Goldman-Cecil Medicine: "New, acute, often ongoing pain may indicate an acute myocardial infarction, unstable angina, or aortic dissection; a pulmonary cause such as acute pulmonary embolism or pleural irritation; a musculoskeletal condition; or a gastrointestinal abnormality such as esophageal reflux or spasm."

The way to organize this in your head is by system and timing:

The "CARDIAC" Mnemonic for Chest Pain Causes

C - Coronary (ACS: STEMI, NSTEMI, Unstable Angina; Stable Angina)
A - Aortic (Dissection, Aneurysm)
R - Respiratory (PE, Pneumothorax, Pleuritis, Pneumonia)
D - Digestive/GI (GERD, Esophageal spasm, Peptic ulcer, Cholecystitis)
I - Inflammatory/Pericardial (Pericarditis, Myocarditis)
A - Another cardiac cause (Valvular - especially AS; HCM)
C - Chest wall / MSK (Costochondritis, rib fracture, Tietze syndrome)

How to Rule In / Rule Out Each:

ACS (MI/Unstable Angina):

Rule IN: Central/retrosternal, crushing, radiation to jaw/left arm, diaphoresis, nausea, exertion-related or at rest, duration >20 min, diabetic/hypertensive/smoker, male >45 or female >55
Rule OUT: Sharp character, positional (better/worse with position change), fully reproducible on palpation, age <30 with no risk factors, immediate relief with antacids

Aortic Dissection:

Rule IN: Sudden onset, tearing/ripping quality, radiates to the back, hypertension history, Marfan habitus, unequal blood pressures in both arms, pulse deficit
Rule OUT: Gradual onset, no radiation to back, no HTN history, normal and equal pulses

Pulmonary Embolism:

Rule IN: Pleuritic chest pain (worse on inspiration), dyspnea, recent immobility/long travel/surgery, DVT symptoms (calf swelling/tenderness), oral contraceptive use, hemoptysis, tachycardia out of proportion
Rule OUT: No pleuritic character, no risk factors, no tachycardia, normal O2 saturation

Pericarditis:

Rule IN: Sharp pain, worse lying flat, better leaning forward (sitting up), recent viral illness/fever, friction rub on auscultation, saddle-shaped ST elevation on ECG
Rule OUT: Crushing character, radiation to arm, no positional variation, no preceding fever

GERD/Esophageal:

Rule IN: Burning quality, lower retrosternal, worse after meals/lying down, relieved by antacids, associated regurgitation/waterbrash
Rule OUT: Radiation to jaw/arm, diaphoresis, ECG changes

MSK/Chest Wall:

Rule IN: Reproducible on palpation of chest wall, localized, worsened by movement, recent cough/trauma
Rule OUT: Not reproducible, radiation to arm, associated autonomic symptoms

DYSPNEA - Is It Heart or Lungs?

Goldman-Cecil puts it clearly: "Dyspnea is commonly caused by cardiovascular or pulmonary disease. A systematic approach with selected tests nearly always reveals the cause."

Key differentiating features:

Feature	Cardiac	Respiratory
Onset	Exertional, then at rest	Usually with infections/allergens
Orthopnea (worse lying flat)	Yes - classic for LVF	Not typical (except COPD)
PND (wakes at night gasping)	Yes - classic LVF	Rare
Associated ankle edema	Yes (biventricular HF)	Not typical
Wheeze	Can occur (cardiac asthma)	Very common in asthma/COPD
Sputum	Frothy pink (pulmonary edema)	Purulent (infection), clear (asthma)
Precipitant	Exertion, lying flat	Cold air, allergens, infections

The "hunger for air" feeling (can't get enough air in) points cardiac. Effort to breathe/tight chest with wheeze points pulmonary. (Goldman-Cecil Medicine)

PALPITATIONS - Cardiac or Not?

From Goldman-Cecil: "Palpitations describe a subjective sensation of an irregular or abnormal heartbeat. They should be defined in terms of duration and frequency, precipitating factors, and associated symptoms of chest pain, dyspnea, lightheadedness, or syncope."

Your key questions:

Regular or irregular? (Regular = SVT/VT; Irregularly irregular = AF)
Sudden start and stop vs. gradual? (Sudden = re-entry SVT; Gradual = sinus tachycardia)
Associated syncope, chest pain, dyspnea? If yes → mandatory urgent workup
Triggers: caffeine, stress, exercise, thyroid meds?
"Flip-flop/skipped beat" = isolated ectopics (benign)
Rate: if patient can tap it out - fast and regular = SVT; fast and irregular = AF

Non-cardiac causes to rule out: Thyrotoxicosis, anemia, anxiety, fever, dehydration (sinus tachycardia), caffeine/drug use

SYNCOPE - The Most Important Branching Point

Goldman-Cecil: "Syncope caused by a cardiac arrhythmia usually occurs with little warning. Syncope with exertion or just after conclusion of exertion is typical of aortic stenosis and hypertrophic obstructive cardiomyopathy."

Three big categories:

Type	Key Features	Cause
Cardiac syncope	No warning / sudden, during exertion, post-exertion, associated palpitations, ECG abnormality, structural heart disease	Arrhythmia, AS, HCM, cardiac tamponade
Vasovagal / Reflex	Prodrome (nausea, warmth, sweating), standing/emotional trigger, quick recovery, young patient	Vagal reflex
Orthostatic	On standing, dehydration, elderly, antihypertensives, > 20 mmHg BP drop	Autonomic/volume
Neurological	Seizure activity, post-ictal confusion, focal deficits, headache	TIA, seizure, migraine

Red flags that mean cardiac until proven otherwise: Syncope during exertion, syncope without prodrome, family history of sudden cardiac death in young family member, known structural heart disease, ECG abnormality.

EDEMA - Is It Cardiac?

Cardiac edema characteristics:

Bilateral, pitting, dependent (ankles/legs, worse at end of day)
Associated JVD (raised JVP), orthopnea, PND, S3 gallop
Often with ascites and hepatomegaly (right heart failure)

Rule out non-cardiac causes:

Unilateral edema → DVT or local venous/lymphatic obstruction
Hypoalbuminemia (nephrotic syndrome, liver cirrhosis, malnutrition) → bilateral but no JVD
Hypothyroidism → non-pitting myxedema
Drug-induced (calcium channel blockers, NSAIDs) → dependent, bilateral, no JVP rise

Step 4: The Multi-System Cross-Check (Ruling Out Other Systems)

This is exactly what you asked - "how do I rule out that it's RS, CNS, GI, not cardiology?"

After your initial assessment, run through this quick checklist mentally:

Is it really cardiac or could it be...

System	Mimics	Key Distinguisher
Respiratory	PE, pneumothorax, pleuritis	Pleuritic pain (inspiration), signs of consolidation, wheeze, no radiation to arm
GI	GERD, esophageal spasm, peptic ulcer, cholecystitis	Meals-related, antacid-relief, epigastric, no radiation to arm, no sweating
MSK	Costochondritis, Tietze, rib fracture	Reproducible on palpation, no autonomic symptoms, positional/movement-related
Neurological	Herpes zoster (pre-rash), anxiety/panic	Dermatomal distribution, no ECG changes, look for rash, situational triggers
Metabolic	Thyroid disease, anemia, electrolyte disturbance	Systemic symptoms (heat intolerance, weight change, pallor), bloods

Step 5: Your Risk Stratification Habit

For every cardiac case, mentally note:

Risk factors present?

Hypertension, Diabetes, Dyslipidemia, Smoking, Obesity, Family history of CAD (1st-degree relative <55M or <65F), Previous MI/PCI/CABG

The more of these present, the higher your suspicion for ischemic heart disease as the cause of any symptom.

Step 6: The Investigations Sequence (Completing Your Differential)

After history and examination, here is the standard first-line battery:

ECG - always first; ST changes, arrhythmia, LVH, axis, bundle branch block
Chest X-ray - cardiomegaly, pulmonary edema (bat-wing/Kerley B lines), widened mediastinum (dissection), consolidation, pneumothorax
Troponin - cardiac biomarker for myocardial injury
BNP/NT-proBNP - for heart failure
Echo - ventricular function, valves, wall motion, pericardial effusion
Bloods - CBC (anemia), TFTs (thyroid), RFTs, LFTs, D-dimer (PE), lipid profile

The investigations do not replace your clinical reasoning - they confirm what your history and exam have already narrowed down to.

The Mental Model Summary: "SPOT the Diagnosis"

Use this as your mental checklist at every clinic encounter:

S - Symptoms: What exactly is the patient feeling? (SOCRATES each one)
P - Pattern: Acute vs. chronic? Exertional vs. rest? Positional?
O - Origin: Which system? Cardiac / Respiratory / GI / MSK / Neuro / Metabolic?
T - Triggers/Risk factors: What makes it worse/better? What risk factors exist?

Then give your 3-5 differential diagnoses in order of most likely to most dangerous (you must always consider the most dangerous diagnosis even if less likely).

A Worked Example: Chest Pain in Clinic

Patient: 58M, smoker, hypertensive, comes in with central chest tightness for 3 hours, radiating to left arm, with sweating and nausea, not relieved by rest.

Your thinking:

Problem representation: Older male, high-risk background, acute-onset central crushing chest pain with radiation and autonomic symptoms, lasting hours, not settling
Most dangerous diagnosis first: ACS (STEMI/NSTEMI) - fits perfectly
Next dangerous: Aortic dissection - but no tearing quality, no back radiation, no pulse deficit → less likely, but get BP both arms
PE - no pleuritic features, no risk factors beyond smoking → low probability
Pericarditis - no positional relief on leaning forward, no recent fever → unlikely
GI/MSK - no meals relationship, sweating and radiation don't fit → unlikely

Verdict: Likely ACS. ECG immediately. Troponin. Aspirin. Call cardiology.

For Murmurs Specifically

Since you mentioned murmurs are difficult - here is the one-line approach:

Every murmur: describe → localize → time → grade → radiate

Murmur	Location	Timing	Radiation	Key Feature
AS	Aortic area (2nd R ICS)	Systolic ejection	Carotids	Slow-rising pulse, exertional syncope/chest pain
MR	Mitral area (apex)	Pansystolic	Axilla	Associated with AF, dyspnea
MVP	Apex	Mid-systolic click + late systolic murmur	-	Click heard, young females
AR	Left sternal border	Early diastolic	-	Wide pulse pressure, collapsing pulse
MS	Apex	Mid-diastolic rumble	-	Opening snap, AF, history of rheumatic fever
TR	Tricuspid (4th L ICS)	Pansystolic	-	JVP raised, pulsatile liver

The key takeaway: you will never go blank again if you have a system. The knowledge is already in your head from the textbooks - the clinical framework just gives it a structure to come out in the right order. Practice presenting cases to yourself using the SOCRATES + SPOT approach even when reading theory, and the clinic will start feeling natural.

Sources: Goldman-Cecil Medicine International Edition (Cardinal Symptoms of Cardiovascular Disease, Chapter 39; Heart Failure Diagnosis, Chapter 45); Rosen's Emergency Medicine (Chest Pain, Chapter 165); Goldman-Cecil Medicine (Syncope, Palpitations, Dyspnea)

Similarly for cns

Same framework, now for CNS. Let me pull the textbook content on neurological symptoms and clinical approach.

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Excellent content. I have rich material from Neuroanatomy through Clinical Cases and Harrison's. Now let me compile the full CNS framework.

How to Think Like a Doctor in CNS: A Clinical Reasoning Framework for MBBS Students

CNS is where most students panic the most - because it feels like the exam is localization + anatomy + differentials all at once. But there is one master key that unlocks all of neurology:

"Where is the lesion?" comes before "What is the lesion?"

You always localize first, then list differentials for that location. If you do this in the right order, you will never go blank.

The Master Framework: Two Questions Before Any Differential

Question 1: WHERE is the lesion? Cerebral cortex → Brainstem → Cerebellum → Spinal cord → Peripheral nerve → Neuromuscular junction → Muscle

Question 2: WHAT is the time course? Seconds-minutes (vascular) → Hours-days (infection/inflammatory) → Weeks-months (tumor/demyelinating) → Years (degenerative)

These two answers alone narrow your differential from 100 possibilities to 4 or 5.

Step 1: The Cardinal Symptoms of Neurology

Every CNS presentation will involve one or more of these:

Headache
Weakness / Paralysis
Altered consciousness / Confusion / Coma
Seizures
Sensory disturbance (numbness, tingling, pain)
Vertigo / Dizziness / Imbalance
Visual disturbance (diplopia, loss of vision, field defect)
Speech disturbance (dysarthria, aphasia)
Involuntary movements / Tremor
Memory / Cognitive changes

Step 2: The Localization Principle (The Most Important Skill in Neurology)

Before differentials, you must know which level of the neuraxis is affected. The physical signs tell you this automatically.

UMN vs LMN - The Foundation

From Neuroanatomy through Clinical Cases (Table 6.4):

Sign	UMN Lesion	LMN Lesion
Weakness	Yes	Yes
Atrophy	No	Yes
Fasciculations	No	Yes
Reflexes	Increased (hyperreflexia)	Decreased (areflexia)
Tone	Increased (spasticity)	Decreased (flaccidity)
Plantar response	Upgoing (Babinski +ve)	Downgoing

UMN = lesion from cortex down to anterior horn cell (brain, brainstem, spinal cord) LMN = lesion from anterior horn cell outward (anterior horn, nerve root, plexus, peripheral nerve)

This single table tells you more than memorizing 50 diseases. If a patient has weakness + brisk reflexes + Babinski + spasticity = UMN. If weakness + wasting + fasciculations + flaccidity = LMN.

The Weakness Pattern Map

From Harrison's Principles (22E):

Pattern of Weakness	Most Likely Level	Think of...
Hemiparesis (one side face + arm + leg)	Contralateral hemisphere or brainstem	Stroke, hemorrhage, tumor, abscess
Paraparesis (both legs)	Spinal cord (bilateral)	Spinal cord compression, MS, myelitis
Monoparesis (one limb)	LMN usually - root/plexus/nerve	Disc prolapse, entrapment neuropathy; occasionally cortex
Quadriparesis (all four limbs)	High cervical cord or brainstem	Cervical myelopathy, GBS, myasthenia gravis
Proximal weakness (shoulders/hips)	Muscle or NMJ	Myopathy, myasthenia gravis
Distal weakness (hands/feet)	Peripheral nerve	Peripheral neuropathy (DM, alcohol, GBS)
Bulbar weakness (face, speech, swallow)	Brainstem or NMJ	Brainstem stroke, MND, myasthenia

Step 3: Chief Complaint by Chief Complaint

HEADACHE - The Most Common Presentation

The most critical question is: Is this a primary headache or a secondary (dangerous) headache?

From Neuroanatomy through Clinical Cases: "Although usually benign, headache occasionally signals life-threatening conditions."

The "SNOOP" Red Flags - Secondary Headache Until Proven Otherwise

Letter	Red Flag	Think of...
S	Systemic signs (fever, weight loss, HIV, cancer)	Meningitis, brain abscess, metastasis
N	Neurological signs (focal deficit, papilloedema, confusion)	Raised ICP, hemorrhage, tumor
O	Onset sudden ("thunderclap")	Subarachnoid hemorrhage (SAH) - "worst headache of my life"
O	Onset after 50 years	Giant cell arteritis, intracranial malignancy
P	Progressive worsening, or Postural (worse lying flat)	Space-occupying lesion, raised ICP

If none of these red flags are present, you can consider primary headache. If any is present, investigate urgently.

Primary Headache Differential (Goldman-Cecil Table 367-3)

Type	Character	Side	Duration	Associated Features	Key Distinguisher
Migraine	Throbbing, moderate-severe	Unilateral (but not always)	Hours to days	Photophobia, phonophobia, nausea/vomiting, aura	Worsens with activity, relieved by sleep/dark room
Tension	Tight band-like, dull	Bilateral	Hours to days	No nausea, minimal photo/phonophobia	Improves with activity (opposite of migraine)
Cluster	Severe, stabbing, periorbital	Unilateral	15 min-3 hours	Ipsilateral ptosis, miosis, rhinorrhea, tearing	"Suicide headache," occurs at same time daily, male

Secondary Headache - Dangerous Differentials

Condition	Onset	Key Feature	Emergency?
SAH	Thunderclap, instantaneous	"Worst headache ever," neck stiffness, photophobia	YES - CT immediately
Bacterial meningitis	Hours	Fever + headache + neck stiffness (Kernig/Brudzinski) ± rash (meningococcal)	YES
Raised ICP / SOL	Gradual, progressive	Morning headaches, worse bending/coughing, papilloedema, vomiting without nausea	Urgent
Venous sinus thrombosis	Subacute	Headache + focal deficits + seizures, post-partum/OCP use	Urgent
Giant cell arteritis	Age >50	Temporal tenderness, jaw claudication, visual loss, ESR very high	Urgent (steroid immediately)
Hypertensive crisis	With high BP	Occipital headache, BP >180/120	Urgent

Your rule: Every new, severe, or "first and worst" headache is SAH until proven otherwise. CT brain immediately.

WEAKNESS / PARALYSIS - The Localizer

Use the two-step approach:

Is it UMN or LMN? (reflexes, tone, atrophy tell you)
What is the distribution? (hemi/para/mono/quad tells you the level)

Acute-Onset Weakness - Think Vascular First

Stroke vs Mimics:

Feature	Stroke/TIA	Todd's Palsy (post-seizure)	Hemiplegic Migraine	MS relapse
Onset	Seconds-minutes	After witnessed seizure	With headache/aura	Hours-days
Recovery	Persists (TIA <24h)	Clears in hours	Clears with headache	Incomplete/relapsing
Age/Risk factors	Older, vascular RF	Any, known epilepsy	Young, family history	Young female, multiple episodes
MRI	DWI positive	Negative or post-ictal changes	Negative	White matter lesions

Stroke Territory = Localization:

Middle cerebral artery (MCA): contralateral hemiplegia (face + arm > leg) + aphasia (if dominant)
Posterior cerebral artery (PCA): contralateral homonymous hemianopia ± memory loss
Anterior cerebral artery (ACA): contralateral leg > arm weakness
Brainstem: crossed signs (ipsilateral CN palsy + contralateral hemi) = classic brainstem stroke
Cerebellar: ataxia + nystagmus + dysarthria, NO weakness

The "FAST" warning for stroke you already know - Face, Arm, Speech, Time. Add "BE-FAST": Balance + Eyes (visual) + FAST.

Subacute Weakness (weeks)

Symmetrical ascending weakness, areflexia, preceded by infection → Guillain-Barré Syndrome
Proximal weakness, fatigue, female, diplopia/ptosis worse at end of day → Myasthenia Gravis
Progressive weakness with UMN + LMN mixed + no sensory loss → Motor Neuron Disease (ALS)
Multiple episodes, young female, different areas → Multiple Sclerosis

ALTERED CONSCIOUSNESS / COMA

The approach here is structured: Is it structural or metabolic?

Feature	Structural (focal brain lesion)	Metabolic / Toxic / Systemic
Onset	Usually sudden (bleed) or subacute (infection)	Gradual, fluctuating
Focal signs	Yes - hemiparesis, unequal pupils, gaze deviation	Absent (or symmetric)
Pupils	Asymmetric, unreactive (herniation)	Symmetric, reactive (usually)
Preceding history	Trauma, headache, focal symptoms	Fever, drugs, DM, renal/liver disease
CT scan	Abnormal	Usually normal (or diffuse change)

Metabolic causes of coma - use "AEIOU TIPS":

A - Alcohol / Acidosis
E - Epilepsy (post-ictal)
I - Insulin (hypo/hyperglycemia)
O - Opiates / Overdose
U - Uremia (renal failure)
T - Trauma
I - Infection (septic encephalopathy, meningitis)
P - Psychiatric / Psychogenic
S - Stroke / Shock / Structural

The Glasgow Coma Scale (GCS) - always document Eyes (1-4) + Verbal (1-5) + Motor (1-6).

Immediate urgent question: Is there raised ICP? Signs: Cushing's triad (hypertension + bradycardia + irregular breathing), papilloedema, blown (dilated) pupil. This is a neurosurgical emergency.

SEIZURES

Your first question: Is this actually a seizure?

Seizure vs Syncope vs Pseudoseizure:

Feature	Seizure	Vasovagal Syncope	Pseudoseizure
Onset	May have aura	Prodrome (nausea, blackout, warmth)	Gradual, often emotional trigger
Movements	Tonic-clonic, rhythmic	Myoclonic jerks (brief, end of faint)	Non-rhythmic, asynchronous, may wax and wane
Duration	Typically <5 min	Seconds	Often prolonged
Post-ictal confusion	Yes - lasting minutes-hours	No - rapid recovery	No
Tongue bite	Yes (lateral)	Rarely	No
Incontinence	Sometimes	Rarely	Rarely
EEG	Abnormal	Normal	Normal

Once confirmed as seizure, classify it:

Focal (one part of body twitching, staring, automatisms) → cortical origin → look for structural cause (tumor, scar, cortical dysplasia)
Generalized tonic-clonic from onset → epilepsy syndrome, metabolic, drug withdrawal

Causes by age:

Neonate: birth asphyxia, hypoglycemia, hypocalcemia, meningitis
Child: febrile seizure (benign), epilepsy syndromes
Young adult: epilepsy, drugs/alcohol, head trauma
Elderly: stroke, tumor, metabolic (Na/glucose/Ca abnormality), drugs

Always check: Blood glucose FIRST (hypoglycemia is the most treatable and reversible cause).

VERTIGO - Peripheral or Central?

This is a common clinical trap. The key: not all dizziness is vertigo, and not all vertigo is inner ear.

First define the dizziness:

True vertigo (room spinning) vs Pre-syncope (about to faint) vs Disequilibrium (unsteady walking) vs Non-specific dizziness

If true vertigo:

Feature	Peripheral (Inner ear)	Central (Brainstem/Cerebellum)
Onset	Sudden	Gradual or sudden
Severity	Severe	Moderate
Nausea/Vomiting	Marked	Mild
Nystagmus	Horizontal, fatigable, unidirectional	Vertical, non-fatigable, direction-changing
Hearing loss / Tinnitus	Often present (if cochlea involved)	Absent
Neurological signs	Absent	Present (diplopia, dysphagia, ataxia, facial numbness)
HINTS exam	Negative (safe)	Positive (dangerous)

Peripheral causes: BPPV (most common - triggered by head movement, Dix-Hallpike positive), Vestibular neuritis (after viral illness, continuous days), Meniere's disease (triad: episodic vertigo + tinnitus + sensorineural hearing loss)

Central causes: Posterior circulation stroke (PICA/AICA territory), MS, cerebellar tumors, Wallenberg syndrome

Red flag: Any vertigo with neurological signs = central = MRI brain urgently.

SPEECH DISTURBANCE - Dysarthria vs Aphasia

This distinction is immediate localization:

Type	What it is	Localization
Dysarthria	Slurred/garbled speech, but language is intact	Motor pathway - brainstem, cerebellum, LMN (bulbar palsy)
Aphasia	Language itself is broken (can't find words, or can't understand)	Dominant hemisphere (left in 95% of right-handers)
Dysphonia	Hoarse voice, but speech is normal	Larynx or vagus nerve

Aphasia types:

Broca's (frontal): non-fluent, broken output, comprehension preserved. Patient is frustrated (knows what they want to say)
Wernicke's (temporal): fluent, meaningless jargon, comprehension broken. Patient seems unaware
Global: both areas - severe, non-fluent, poor comprehension

Step 4: The Time Course Rule (Locks In Your Pathology)

Time Course	Pathology	Examples
Seconds to minutes	Vascular	Stroke, TIA, SAH, syncope
Minutes to hours	Vascular (evolving) / Toxic / Metabolic	Evolving stroke, hypoglycemia, drug toxicity
Hours to days	Infection / Inflammatory	Bacterial meningitis, encephalitis, GBS early
Days to weeks	Demyelinating / Autoimmune	MS relapse, ADEM, autoimmune encephalitis
Weeks to months	Neoplasm / Abscess / Subacute infection	Brain tumor, TB meningitis, subdural hematoma
Months to years	Degenerative	Parkinson's, Alzheimer's, MND, hereditary ataxia

Step 5: The Multi-System Cross-Check - "Is This Really CNS?"

Just like we did for cardiology, here is how to rule out other systems mimicking CNS:

System	Mimics CNS	Key Distinguisher
Cardiac	Syncope mistaken for seizure	No post-ictal confusion, rapid recovery, cardiac history
Metabolic	Hypoglycemia = any neuro sign imaginable	Check blood glucose FIRST in every altered patient
Psychiatric	Conversion/functional disorder, psychosis	Inconsistent exam, normal investigations, stressors, la belle indifférence
Ophthalmic	Visual loss (retinal artery occlusion vs cortical)	Monocular (eye) vs binocular (cortex/chiasm)
ENT	Peripheral vertigo vs brainstem	Absent neurological signs, HINTS exam negative
Endocrine	Thyroid encephalopathy, adrenal crisis	Systemic features, metabolic bloods abnormal

Step 6: The Investigations Sequence in Neurology

Investigation	Use it for
CT brain (non-contrast)	First-line for acute headache (SAH), trauma, stroke rule-out, raised ICP
MRI brain	Better for brainstem, posterior fossa, demyelination, early infarct (DWI)
Lumbar puncture (LP)	After CT clears raised ICP - meningitis (cells, protein, glucose, culture), SAH (xanthochromia), GBS
EEG	Seizure diagnosis, encephalopathy
EMG/NCS	LMN lesions - peripheral nerve, NMJ, muscle
Blood tests	Glucose, electrolytes (Na, Ca), renal/liver, TFTs, B12, CBC, ESR/CRP, autoimmune screen
Echo + carotid Doppler	Cardioembolic stroke workup

Step 7: A Worked Example - CNS in the Clinic

Patient: 28-year-old female, no past history, presents with sudden severe headache while at work, "like a bat hit my head," associated with neck stiffness and photophobia, GCS 14.

Your thinking:

Problem representation: Young woman, thunderclap headache of sudden onset, meningism (neck stiffness + photophobia), slightly altered GCS
Is this primary or secondary? - Red flag: thunderclap onset = secondary until proven otherwise
Most dangerous diagnosis first: Subarachnoid hemorrhage (SAH) - "worst headache ever" + thunderclap + meningism = SAH until proven otherwise
Next dangerous: Bacterial meningitis - also has fever? Rash? Check. Different from SAH by fever + purpuric rash + more infective prodrome
Venous sinus thrombosis - focal signs? Papilloedema? Less acute. Rule out by imaging
Migraine - NO. Thunderclap onset eliminates primary migraine diagnosis. Never diagnose migraine at first presentation with thunderclap character.

Action: CT brain IMMEDIATELY. If CT negative, LP at 12 hours (xanthochromia for SAH). Blood cultures before antibiotics if meningitis considered.

The Mental Scaffold Summary for CNS

Every CNS case: ask these 4 questions in order before giving differentials:

Where? - Localize the lesion (UMN/LMN, level of neuraxis, distribution of weakness)
When? - Time course (vascular / infective / inflammatory / neoplastic / degenerative)
What else? - Any red flags, associated symptoms across systems
Who? - Age + risk factors (young female + relapsing = MS; elderly + vascular RF = stroke; child + fever = meningitis)

Then give your top 3 differentials: most likely → most dangerous → not to miss

Quick-Reference: CNS Red Flags That Are Always Emergencies

Symptom	Red Flag Feature	Emergency Diagnosis
Headache	Thunderclap, "worst ever"	SAH
Headache + Fever + Neck stiffness	Any combination	Bacterial meningitis
Focal deficit + sudden onset	Contralateral face/arm/leg	Stroke
Confusion + focal signs + fever	Temporal lobe features	Herpes encephalitis
Diplopia + ptosis + dilated pupil	CN III palsy	Posterior communicating artery aneurysm
Altered consciousness + Cushing's triad	HTN + bradycardia + irregular breathing	Raised ICP / Herniation
Quadriparesis + ascending	After GI/respiratory infection	Guillain-Barré Syndrome

Sources: Neuroanatomy through Clinical Cases, 3rd Edition (KCC 5.1 Headache; Table 6.4 UMN/LMN Signs; Table 6.5 Weakness Terms); Harrison's Principles of Internal Medicine 22E (Chapter 26, Approach to Weakness, Table 26-2); Goldman-Cecil Medicine (Chapter 367, Table 367-3 Differential Diagnosis of Headache); Plum and Posner's Diagnosis and Treatment of Stupor and Coma

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