🧠 Clinical Vignette — Spot the Diagnosis
📋 HISTORY
👴 70-year-old male
🤢 2 episodes of vomiting
😵 Delirium for 6 hours
⚡ Single tonic-clonic seizure in ER
✅ No upper GIT complaints per relatives
🩺 EXAMINATION
🧠 Altered mental status / delirium
⚡ Witnessed tonic-clonic seizure in ER
👴 Elderly high-risk patient (70 years)
🔬 INVESTIGATIONS
🧪 Serum Sodium: 112 mmol/L
🩸 Random Blood Sugar: 5 mmol/L
❓ WHAT IS THE MOST LIKELY DIAGNOSIS?
✅ Answer & Explanation
KEY FINDING
離 Serum Sodium = 112 mmol/L (Normal: 135–145 mmol/L)
喝 Random Blood Sugar = 5 mmol/L ✅ Normal
⚠️ Na¹ <125 mmol/L → Severe Hyponatremia with neurological features
WHY EACH OPTION?
B
Severe Hyponatremia ✔️
Na¹ = 112 mmol/L → cerebral edema → delirium + seizure. Classic presentation in elderly.
A
Diabetic Ketoacidosis ✘
RBS is normal (5 mmol/L). No hyperglycemia, no ketosis, no Kussmaul breathing.
C
Hypoglycemic Encephalopathy ✘
RBS = 5 mmol/L is normal. Hypoglycemia requires RBS <3.9 mmol/L with symptoms.
D
Hypertensive Encephalopathy ✘
No BP readings provided. Seizure & delirium fully explained by critically low Na¹.
TEACHING POINT
⚡ Na¹ <120 mmol/L → neurological emergency
易 Symptoms: confusion → seizures → coma
Tx: Hypertonic saline (3% NaCl) — correct slowly to avoid ODS
⚠️ Rate: raise Na¹ by max 8–10 mmol/L per 24 hrs
FAQ — Hyponatremia (10 Questions)
1What is hyponatremia?
Hyponatremia is serum sodium <135 mmol/L. It is the most common electrolyte disorder in clinical practice. Severe hyponatremia (Na¹ <120 mmol/L) is a neurological emergency.
2What are the types of hyponatremia?
Classified by volume status:
Hypovolaemic — vomiting, diarrhoea, diuretics
Euvolaemic — SIADH, hypothyroidism, psychogenic polydipsia
Hypervolaemic — heart failure, cirrhosis, nephrotic syndrome
Hypovolaemic — vomiting, diarrhoea, diuretics
Euvolaemic — SIADH, hypothyroidism, psychogenic polydipsia
Hypervolaemic — heart failure, cirrhosis, nephrotic syndrome
3What are the symptoms?
Mild (Na 130–135): nausea, headache, fatigue
Moderate (Na 120–130): confusion, vomiting, lethargy
Severe (<120): seizures, coma, respiratory arrest — due to cerebral oedema
Moderate (Na 120–130): confusion, vomiting, lethargy
Severe (<120): seizures, coma, respiratory arrest — due to cerebral oedema
4What is the most common cause?
SIADH (Syndrome of Inappropriate ADH secretion) is the most common cause of euvolaemic hyponatremia. Triggers include pneumonia, CNS disorders, SSRIs, carbamazepine, and small cell lung cancer.
5How is it investigated?
離 Serum Na¹, K¹, osmolality
離 Urine Na¹ and urine osmolality
喝 TFTs, cortisol, LFTs, RFTs
Urine Na¹ >20 + Urine Osm >100 → suggests SIADH
離 Urine Na¹ and urine osmolality
喝 TFTs, cortisol, LFTs, RFTs
Urine Na¹ >20 + Urine Osm >100 → suggests SIADH
6What is the treatment for severe hyponatremia?
3% Hypertonic Saline — for symptomatic cases (seizures, coma).
Raise Na¹ by 1–2 mmol/L/hr until symptoms resolve, then max 8–10 mmol/L per 24 hrs to prevent ODS.
Raise Na¹ by 1–2 mmol/L/hr until symptoms resolve, then max 8–10 mmol/L per 24 hrs to prevent ODS.
7What is ODS and why does it matter?
Osmotic Demyelination Syndrome (ODS) — caused by overly rapid correction of chronic hyponatremia. Features: dysarthria, dysphagia, quadriplegia, locked-in syndrome. It is irreversible — correction must not exceed 10 mmol/L/24 hrs.
8How is SIADH treated?
1st line: Fluid restriction (500–1000 mL/day)
2nd line: Demeclocycline or urea
3rd line: Vaptans (tolvaptan) — V2 receptor antagonists
Always treat the underlying cause
2nd line: Demeclocycline or urea
3rd line: Vaptans (tolvaptan) — V2 receptor antagonists
Always treat the underlying cause
9Which drugs commonly cause hyponatremia?
SSRIs (fluoxetine, sertraline) — via SIADH
Carbamazepine / oxcarbazepine — via SIADH
Thiazide diuretics — hypovolaemic mechanism
NSAIDs, antipsychotics, PPIs
Carbamazepine / oxcarbazepine — via SIADH
Thiazide diuretics — hypovolaemic mechanism
NSAIDs, antipsychotics, PPIs
10Which patients are at highest risk?
Elderly — reduced renal concentrating ability
Post-operative — ADH surge from stress and pain
Marathon runners — excess hypotonic fluid intake
Patients on thiazides, SSRIs, or carbamazepine
Post-operative — ADH surge from stress and pain
Marathon runners — excess hypotonic fluid intake
Patients on thiazides, SSRIs, or carbamazepine
#Hyponatremia
#LowSodium
#SIADH
#ElectrolyteImbalance
#InternalMedicine
#ClinicalMedicine
#Nephrology
#MedicalEducation
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