I-HUMAN CASE STUDY EXAMINING: SIADH linked to Small
Cell Lung Cancer
Patient Profile
Patient ID:Lucas
Age: 75 years
Gender: Male
Occupation: Retired teacher
Presenting Complaint
Acute confusion and a generalized tonic–clonic seizure at home.
History of Presenting Illness (HPI)
Lucas is a 75-year-old man brought to the emergency department after he was found confused
and later had a generalized tonic–clonic seizure at home. Family report 2 weeks of progressive
lethargy, decreased appetite, nausea, and episodic headaches. Over the past month he has
experienced increasing forgetfulness and reduced exercise tolerance. Family also notes a 5-kg
unintentional weight loss in 3 months and a chronic cough that has worsened in the last 6 weeks.
No recent diuretic use is reported. He has a history of chronic tobacco smoking (50 pack-years),
hypertension (on amlodipine), and benign prostatic hyperplasia. No known history of heart
failure, cirrhosis, or renal disease.
Past Medical History
Hypertension — on amlodipine
BPH — on tamsulosin
Long history of tobacco smoking (quit 1 year ago)
Family History
No known family history of lung cancer. Father died of stroke at age 82.
Social History
1
,I-HUMAN CASE STUDY EXAMINING: SIADH linked to Small
Cell Lung Cancer
Retired teacher, lives with spouse, independent in activities of daily living until recently. Long-
term smoker, occasional alcohol use.
Review of Systems (ROS)
Constitutional: Weight loss, fatigue.
Respiratory: Chronic cough, occasional hemoptysis (small amounts).
Neurological: Headaches, confusion, new seizure.
Cardiovascular: No chest pain or palpitations.
GI/GU: Nausea, decreased appetite.
Physical Examination
General: Elderly male, drowsy but arousable, confused.
Vitals: T 36.8°C, HR 88 bpm, BP 140/85 mmHg, RR 18/min, SpO2 96% on room air.
HEENT: No focal cranial nerve deficits.
Cardiovascular: Normal S1/S2, no murmurs.
Respiratory: Reduced breath sounds with dullness to percussion at the right upper chest;
scattered wheeze.
Abdomen: Soft, non-tender.
Neurological: Confused, no focal limb weakness. Normal reflexes. Post-ictal drowsiness.
Initial Investigations
Serum electrolytes: Na+ 118 mmol/L (low), K+ 4.1 mmol/L, Cl- 90 mmol/L, HCO3- 24
mmol/L.
Serum osmolality: 250 mOsm/kg (low).
Urine osmolality: 520 mOsm/kg (inappropriately high).
Urine sodium: 60 mmol/L (elevated).
Blood urea nitrogen (BUN): 5 mmol/L (low-normal).
2
,I-HUMAN CASE STUDY EXAMINING: SIADH linked to Small
Cell Lung Cancer
Creatinine: 80 µmol/L (normal).
Thyroid function tests: TSH normal.
Cortisol (AM): Normal.
Chest X-ray: Right hilar mass.
CT chest: Right hilar/mediastinal mass consistent with primary lung neoplasm; small pleural
effusion.
ECG: Normal sinus rhythm.
Working Diagnosis
Primary: SIADH (Syndrome of Inappropriate Antidiuretic Hormone secretion) causing
symptomatic hyponatremia.
Likely cause: Paraneoplastic SIADH due to Small Cell Lung Cancer (SCLC).
Diagnostic Reasoning
Lab pattern is consistent with hypotonic hyponatremia (low serum osmolality) with
inappropriately concentrated urine (high urine osmolality) and elevated urine sodium, consistent
with SIADH. Euvolemic examination and normal renal, adrenal, and thyroid function support
SIADH over hypovolemia or endocrine causes. Given smoking history, imaging showing a hilar
mass, and epidemiology, SCLC is the most probable underlying cause.
Management Plan (Initial Acute)
1. Seizure management: Benzodiazepines if actively seizing; otherwise supportive care and
antiepileptic considered after stabilization.
2. Acute correction of severe symptomatic hyponatremia: Hypertonic (3%) saline bolus (e.g.,
100 mL over 10 minutes, repeated up to 2 times as needed) in monitored setting for severe
symptoms (seizure, coma).
3
, I-HUMAN CASE STUDY EXAMINING: SIADH linked to Small
Cell Lung Cancer
3. Careful sodium correction limits: Aim to raise Na+ by no more than 8–10 mmol/L in first 24
hours and <18 mmol/L in first 48 hours to avoid osmotic demyelination.
4. Fluid restriction: 800–1000 mL/day initially.
5. Treat underlying cause: Urgent oncology referral for tissue diagnosis (bronchoscopy/biopsy)
and staging. Small cell lung cancer often responds to chemotherapy and radiotherapy—treatment
can reduce ectopic ADH secretion.
6. Consider pharmacologic therapy if fluid restriction fails: Demeclocycline or vasopressin
receptor antagonists (e.g., tolvaptan) — used judiciously; tolvaptan especially when chronic
hyponatremia and risk of rapid correction is managed.
7. Monitor: Frequent serum sodium measurements (every 2–4 hours during acute correction),
fluid balance, urine output, and neurologic status.
Long-Term Plan
Confirm histology (biopsy).
Oncology staging (CT head, abdomen, PET as indicated) and commence chemo ± radiotherapy.
Ongoing management of chronic hyponatremia and monitoring; consider endocrine consult.
Palliative care involvement if advanced disease.
Follow-up
4
Cell Lung Cancer
Patient Profile
Patient ID:Lucas
Age: 75 years
Gender: Male
Occupation: Retired teacher
Presenting Complaint
Acute confusion and a generalized tonic–clonic seizure at home.
History of Presenting Illness (HPI)
Lucas is a 75-year-old man brought to the emergency department after he was found confused
and later had a generalized tonic–clonic seizure at home. Family report 2 weeks of progressive
lethargy, decreased appetite, nausea, and episodic headaches. Over the past month he has
experienced increasing forgetfulness and reduced exercise tolerance. Family also notes a 5-kg
unintentional weight loss in 3 months and a chronic cough that has worsened in the last 6 weeks.
No recent diuretic use is reported. He has a history of chronic tobacco smoking (50 pack-years),
hypertension (on amlodipine), and benign prostatic hyperplasia. No known history of heart
failure, cirrhosis, or renal disease.
Past Medical History
Hypertension — on amlodipine
BPH — on tamsulosin
Long history of tobacco smoking (quit 1 year ago)
Family History
No known family history of lung cancer. Father died of stroke at age 82.
Social History
1
,I-HUMAN CASE STUDY EXAMINING: SIADH linked to Small
Cell Lung Cancer
Retired teacher, lives with spouse, independent in activities of daily living until recently. Long-
term smoker, occasional alcohol use.
Review of Systems (ROS)
Constitutional: Weight loss, fatigue.
Respiratory: Chronic cough, occasional hemoptysis (small amounts).
Neurological: Headaches, confusion, new seizure.
Cardiovascular: No chest pain or palpitations.
GI/GU: Nausea, decreased appetite.
Physical Examination
General: Elderly male, drowsy but arousable, confused.
Vitals: T 36.8°C, HR 88 bpm, BP 140/85 mmHg, RR 18/min, SpO2 96% on room air.
HEENT: No focal cranial nerve deficits.
Cardiovascular: Normal S1/S2, no murmurs.
Respiratory: Reduced breath sounds with dullness to percussion at the right upper chest;
scattered wheeze.
Abdomen: Soft, non-tender.
Neurological: Confused, no focal limb weakness. Normal reflexes. Post-ictal drowsiness.
Initial Investigations
Serum electrolytes: Na+ 118 mmol/L (low), K+ 4.1 mmol/L, Cl- 90 mmol/L, HCO3- 24
mmol/L.
Serum osmolality: 250 mOsm/kg (low).
Urine osmolality: 520 mOsm/kg (inappropriately high).
Urine sodium: 60 mmol/L (elevated).
Blood urea nitrogen (BUN): 5 mmol/L (low-normal).
2
,I-HUMAN CASE STUDY EXAMINING: SIADH linked to Small
Cell Lung Cancer
Creatinine: 80 µmol/L (normal).
Thyroid function tests: TSH normal.
Cortisol (AM): Normal.
Chest X-ray: Right hilar mass.
CT chest: Right hilar/mediastinal mass consistent with primary lung neoplasm; small pleural
effusion.
ECG: Normal sinus rhythm.
Working Diagnosis
Primary: SIADH (Syndrome of Inappropriate Antidiuretic Hormone secretion) causing
symptomatic hyponatremia.
Likely cause: Paraneoplastic SIADH due to Small Cell Lung Cancer (SCLC).
Diagnostic Reasoning
Lab pattern is consistent with hypotonic hyponatremia (low serum osmolality) with
inappropriately concentrated urine (high urine osmolality) and elevated urine sodium, consistent
with SIADH. Euvolemic examination and normal renal, adrenal, and thyroid function support
SIADH over hypovolemia or endocrine causes. Given smoking history, imaging showing a hilar
mass, and epidemiology, SCLC is the most probable underlying cause.
Management Plan (Initial Acute)
1. Seizure management: Benzodiazepines if actively seizing; otherwise supportive care and
antiepileptic considered after stabilization.
2. Acute correction of severe symptomatic hyponatremia: Hypertonic (3%) saline bolus (e.g.,
100 mL over 10 minutes, repeated up to 2 times as needed) in monitored setting for severe
symptoms (seizure, coma).
3
, I-HUMAN CASE STUDY EXAMINING: SIADH linked to Small
Cell Lung Cancer
3. Careful sodium correction limits: Aim to raise Na+ by no more than 8–10 mmol/L in first 24
hours and <18 mmol/L in first 48 hours to avoid osmotic demyelination.
4. Fluid restriction: 800–1000 mL/day initially.
5. Treat underlying cause: Urgent oncology referral for tissue diagnosis (bronchoscopy/biopsy)
and staging. Small cell lung cancer often responds to chemotherapy and radiotherapy—treatment
can reduce ectopic ADH secretion.
6. Consider pharmacologic therapy if fluid restriction fails: Demeclocycline or vasopressin
receptor antagonists (e.g., tolvaptan) — used judiciously; tolvaptan especially when chronic
hyponatremia and risk of rapid correction is managed.
7. Monitor: Frequent serum sodium measurements (every 2–4 hours during acute correction),
fluid balance, urine output, and neurologic status.
Long-Term Plan
Confirm histology (biopsy).
Oncology staging (CT head, abdomen, PET as indicated) and commence chemo ± radiotherapy.
Ongoing management of chronic hyponatremia and monitoring; consider endocrine consult.
Palliative care involvement if advanced disease.
Follow-up
4
