History Taking · Intermediate · Nephrology

Tiredness and Lethargy in a 58-Year-Old Woman

Practise this PLAB 2 history taking station on SSRI-Induced Hyponatraemia. 8-minute voice AI simulation with feedback on all 3 marking domains.

Clinical scenario

You are an FY2 doctor in general practice. Mrs Karen Dawson, a 58-year-old woman, has come to see you with increasing fatigue and lethargy over the past month. She has been on citalopram for anxiety for six months. Please take a focused history, assess for hyponatraemia as a potential cause of her symptoms, and discuss the role of selective serotonin reuptake inhibitor medications in causing hyponatraemia secondary to Syndrome of Inappropriate Antidiuretic Hormone secretion.

Background notes: PMH: Anxiety, Depression (previous episodes after divorce), Hypothyroidism

What this station tests

  • Connecting SSRI use to hyponatraemia symptoms: fatigue, nausea, headache, and confusion that are attributed to depression returning
  • Not increasing the dose of the causative medication: recognising that escalating citalopram would worsen the hyponatraemia
  • Paired serum and urine osmolality as the diagnostic investigation for SIADH
  • Risk factors for SSRI-induced hyponatraemia: age, female sex, concurrent diuretics, low body weight
  • Switching to an alternative antidepressant with lower hyponatraemia risk (mirtazapine) rather than simply stopping

How to use your 8 minutes

  • 0-1 min — Introduction: Introduce yourself, confirm identity, open question. 'What's brought you in today?'
  • 1-4 min — Systematic History: Presenting complaint detail (SOCRATES for pain, timeline, severity). Systems review. PMH, medications, allergies.
  • 4-6 min — Context and ICE: Social history (smoking, alcohol, occupation, living situation). Family history. Ideas, Concerns, Expectations.
  • 6-7 min — Summary and Plan: Summarise findings back to patient. Share differential/working diagnosis. Outline investigation and management plan.
  • 7-8 min — Closing: Safety netting with specific red flags. Arrange follow-up. Check for questions.

Consultation approach

The opening

Drug-induced hyponatraemia is commonly missed because the symptoms (fatigue, lethargy, nausea) overlap with the condition being treated (depression/anxiety). The candidate must connect the medication timeline to the symptom onset. Mrs Dawson is 58, on citalopram for 6 months, presenting with 1 month of increasing fatigue. She thinks her depression is returning. Open with: 'Mrs Dawson, tell me about the fatigue and when exactly it started in relation to your other treatments.'

Core approach

The diagnostic clue is the timeline. She was started on citalopram 6 months ago for anxiety. The fatigue started 1 month ago, well after the citalopram was initiated. SSRIs can cause hyponatraemia through SIADH at any point during treatment, though typically within the first few weeks to months. Other symptoms of hyponatraemia: nausea, headache, muscle cramps, unsteadiness. She attributes these to depression returning, but they are consistent with low sodium.

She thinks she needs a higher dose of citalopram. This is the critical moment: the candidate must consider the medication as the cause rather than increasing the dose, which would worsen the problem. Ask specifically: 'Have you had any nausea, headaches, or muscle cramps alongside the tiredness?' These symptoms would not be expected from worsening anxiety.

Check for other causes of hyponatraemia. Fluid intake: is she drinking excessively? Diuretic use (she has hypothyroidism on levothyroxine, check for any diuretics). Recent illness with vomiting or diarrhoea. Hypothyroidism itself can cause hyponatraemia if undertreated. Check recent TFTs.

Risk factors for SSRI-induced hyponatraemia: age over 65 (she is 58, borderline), female sex, concurrent diuretics, low body weight. She fits several risk factors.

Closing and safety netting

Explain the concern: 'Mrs Dawson, before we consider changing your citalopram dose, I want to check your sodium level. One of the uncommon side effects of citalopram is that it can lower sodium in the blood, which causes exactly the symptoms you are describing: tiredness, nausea, and difficulty concentrating. If that is the case, the solution is adjusting the medication, not increasing it.'

Investigations: urgent U&E (sodium level), paired serum and urine osmolality (confirms SIADH if serum osmolality low with inappropriately concentrated urine), TFTs (check thyroid replacement adequacy), cortisol (exclude adrenal insufficiency). If confirmed SSRI-induced hyponatraemia: stop citalopram, monitor sodium recovery, and switch to an alternative antidepressant with lower hyponatraemia risk (mirtazapine is often used).

Safety net: 'If you develop confusion, severe headache, or seizures before your blood test, go to A&E immediately.' Arrange bloods within 24 to 48 hours. Follow-up with results.

How examiners mark this station

Examiners will focus on the thoroughness and structure of your history taking for ssri-induced hyponatraemia. Domain 1 (Data Gathering) carries the most weight: expect marks for systematic coverage of presenting complaint, red flags, PMH, medications, social and family history. Domain 2 (Clinical Management) requires a clear differential, appropriate investigations, and a safe management plan with safety netting. Domain 3 (Interpersonal Skills) is assessed throughout: genuine exploration of ICE, active listening, empathic responses, and clear communication without jargon.

Domain 1: Data Gathering, Technical and Assessment Skills (Primary focus)

Scores well: Timeline connecting citalopram to symptoms. Hyponatraemia symptoms actively sought (nausea, headache, cramps). Other causes screened (fluid intake, diuretics, thyroid). Risk factors identified. Medication review.

Costs marks: Not connecting citalopram to symptoms. Accepting depression explanation without bloods. Not checking thyroid.

Domain 2: Clinical Management Skills (Primary focus)

Scores well: Urgent sodium checked before medication change. Paired osmolality planned. Not increasing citalopram. Alternative antidepressant identified (mirtazapine). Severe hyponatraemia safety netting. TFTs checked.

Costs marks: Increasing citalopram. No sodium check. No alternative medication plan. No safety netting.

Domain 3: Interpersonal Skills (Throughout)

Scores well: Explaining why checking bloods comes before medication change. Validating her experience (symptoms are real, but cause may be different). Providing hope (adjusting medication should resolve symptoms).

Costs marks: Dismissing her symptoms. Making her feel the citalopram was wrong from the start. Not explaining the rationale for checking sodium.

Common examiner feedback (and how to fix it)

Did not gather sufficient information to make an adequate assessment of the patient's condition

Fix: Use a consistent framework for every history. After covering the presenting complaint, systematically move through PMH, drug history, social history, family history, and ICE. Keep a mental checklist.

Did not identify the patient's problems and/or did not develop a management plan adequately

Fix: Reserve the final 2 minutes to summarise your findings, share your working diagnosis with the patient, and outline your investigation and management plan including safety netting.

Common mistakes in this station

  1. Increasing the citalopram dose. She thinks her depression is returning. The fatigue, nausea, and poor concentration are consistent with hyponatraemia, not worsening anxiety. Candidates who increase the SSRI without checking sodium worsen the problem.
  2. Attributing the symptoms to depression without checking bloods. Hyponatraemia symptoms overlap with depression symptoms. The only way to distinguish them is a sodium level. Candidates who manage this as a psychiatric presentation miss a medical cause.
  3. Not checking thyroid function. She has hypothyroidism on levothyroxine. Hypothyroidism itself can cause fatigue and hyponatraemia if undertreated. Candidates who do not check TFTs miss a potential contributing factor.

Resitting PLAB 2?

If you have previously struggled with history taking stations, focus on building a consistent systematic framework that you apply to every case. Practise structuring your history into clear phases (presenting complaint, systems review, PMH, social, ICE) so that even under pressure, you cover all domains. Many resitters lose marks not on knowledge but on organisation and time management.

Example opening

Good morning/afternoon, my name is Dr [Name], I'm one of the doctors here today. Could I confirm your name and date of birth please? Thank you. So, what's brought you in to see me today?

Frequently asked questions

What is the best way to take a SSRI-Induced hyponatraemia history in PLAB 2?

Drug-induced hyponatraemia is commonly missed because the symptoms (fatigue, lethargy, nausea) overlap with the condition being treated (depression/anxiety). The candidate must connect the medication timeline to the symptom onset. Mrs Dawson is 58, on citalopram for 6 months, presenting with 1 month of increasing fatigue.

Where are marks won and lost in this SSRI-Induced hyponatraemia station?

Examiners reward: Timeline connecting citalopram to symptoms. Hyponatraemia symptoms actively sought (nausea, headache, cramps). Other causes screened (fluid intake, diuretics, thyroid). Candidates are penalised for: Not connecting citalopram to symptoms. Accepting depression explanation without bloods. Not checking thyroid.

Where do candidates most often go wrong in this station?

Increasing the citalopram dose. She thinks her depression is returning. The fatigue, nausea, and poor concentration are consistent with hyponatraemia, not worsening anxiety.

Can I do well in this station without real-world experience of SSRI-Induced hyponatraemia?

This station rewards process over personal experience. The skill being assessed: Not increasing the dose of the causative medication: recognising that escalating citalopram would worsen the hyponatraemia. Work through the consultation approach above, then rehearse it aloud under the 8-minute time pressure so the structure holds up in the exam.

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