Case 39 A woman suffering dizziness

Cynthia was a 52-year-old woman who had suffered from anxiety and depression for many years. She had been under the local psychiatric services for 16 years. She requested a home visit because she was dizzy and Dr Kirby, a GP registrar, visited her at home. Dr Kirby noted that Cynthia had been unsteady on her feet for several days. She had vomited once. Examination was unremarkable other than that Cynthia’s blood pressure, which dropped from a systolic of 118 mm/hg when sitting to 108 mm/hg on standing. Dr Kirby noted that Cynthia had been started on lisinopril 3 weeks earlier. She advised Cynthia to stop the lisinopril and call again if her dizziness did not improve.

Was there anything else you would have checked?

A week later Cynthia was no better and she called for another visit. Dr Clarke, Dr Kirby’s trainer visited. Dr Clarke noted that Cynthia’s dizziness was not postural. She felt unsteady even sitting in a chair. She had no frank vertigo but had difficulty walking in a straight line, had difficulty drinking a cup of water and appeared a little dehydrated. Dr Kirby noted that Cynthia had been taking lithium for 12 years and arranged for the district nurses to visit and take a serum lithium level.

What would be your differential diagnosis and what would you have done?

The blood lithium level was not available until the following Monday (3 days later) and came back as 1.56 mmol/l. Dr Clarke spoke to the district nurses and established that they were unsure when Cynthia had taken her lithium and therefore whether the test was more than 12 hours after the previous dose. Dr Clarke arranged for the test to be repeated with the blood test to be taken in the morning before Cynthia had taken her daily dose.

The blood test was not taken until the following Thursday. On the Thursday evening Cynthia was seen by Dr Creed from the Out of Hours service. Dr Creed noted that Cynthia was extremely agitated and anxious. She was orientated in time and place but appeared a little dehydrated, with a dry mouth and a resting pulse rate of 100 bpm. Dr Creed wondered about an anxiety disorder or thyrotoxicosis and requested that her own general practitioner visit the following day.

On the Friday morning Dr Clarke received the result that Cynthia’s serum lithium level was 2.15 mmol/l. He arranged her immediate admission. She was treated for lithium toxicity and dehydration but was left with significant ataxia and dysarthria. Cynthia brought a claim against Dr Kirby and Dr Clarke alleging that Dr Kirby had missed the significance of the fact that Cynthia was taking lithium and liable to be suffering from lithium toxicity, and Dr Clarke had suspected the diagnosis but not acted with sufficient alacrity.

Do you think her claim will succeed?

Expert comment

Allegations of failure to monitor drugs, failure to recognize drug toxicity and failure, in particular to monitor serum lithium levels are relatively common causes of claims against general practitioners. Other drugs that occur fairly regularly in claims about monitoring are phenytoin, azathioprine, methotrexate and amiodarone.

In most of the cases the drug will have been started by specialist services and the monitoring then delegated to general practitioners. Patients are on the drugs for many years and the drugs sometimes get overlooked. In the case of lithium toxicity the patients will always have mental health problems and may have defaulted on follow up, and then get lost. Most practices nowadays will regularly audit the few patients they have on lithium and patients who have defaulted will be identified in that way.

Symptoms that are due to drug side effects may be particularly difficult to identify. However, the general practitioner needs to be fully aware of the high risk drugs and high risk symptoms such as breathlessness in the patient on amiodarone, nausea in the patient on azathioprine or ataxia in any drug with cerebellar side effects.

‘Dizziness’ is a common and difficult symptom in primary care. ‘There can be few physicians so dedicated to their art that they do not experience a slight decline in spirits when they learn that their patient’s complaint is giddiness’ (Matthews, 1963). However, a clear history will generally distinguish postural pre syncope (only occurs on standing), frank vertigo – either sustained (possible acute vestibular neuritis) or not sustained and positional (BPPV), light-headedness when not distracted (hyperventilation) or unsteadiness on walking in the elderly, especially on the turn (disequilibrium of the elderly).

In this case one of the key features that Dr Kirby failed to identify was that Cynthia did not have vertigo or postural pre syncope but had both truncal and limb ataxia. If Cynthia had been drinking her clinical features would have been those of alcohol intoxication causing a cerebellar ataxia with cerebellar signs (rolling gait, poor heel-to-toe walking, positive Romberg’s sign, and dysdodokinesis). Cynthia would probably also have been slightly dysarthric. Dr Kirby needed to recognize that, in an unsteady patient on lithium, the condition that you cannot afford to miss is lithium toxicity. The initiation of the ACE inhibitor may have been a precipitant, but once the patient is dehydrated the situation is critical.

Dr Clarke correctly identified the possibility of lithium toxicity but, possibly not unreasonably since he had never encountered it before, failed to realize that the condition is an emergency. He should really have consulted the BNF:

Overdosage, usually with serum-lithium concentration of over 1.5 mmol/litre, may be fatal and toxic effects include tremor, ataxia, dysarthria, nystagmus, renal impairment, and convulsions. If these potentially hazardous signs occur, treatment should be stopped, serum-lithium concentrations redetermined, and steps taken to reverse lithium toxicity. In mild cases withdrawal of lithium and administration of sodium salts and fluid will reverse the toxicity. A serum-lithium concentration in excess of 2 mmol/litre requires urgent treatment.

Neither of the doctors’ actions would be defensible on breach of duty and the irreversible consequences of lithium toxicity are often, as in this case, very serious.

Legal comment

Causation flows from the breach of duty. Thus the MDOs of both Dr Kirby and Dr Clarke will have to settle this claim. The value of the claim will depend on the extent of the dysarthria and ataxia, but it is likely to be several hundred thousand pounds.

The fact that Dr Kirby is a registrar does not excuse his failure. He is expected to act with the same level of competence as a fully qualified general practitioner. The registrar has immediate access to the opinion of the supervising partner and is expected to use this facility whenever it is necessary. If he was in any doubt, he should have referred the matter to his trainer, Dr Clarke. This would have perhaps exonerated him to some extent, but it would not have altered the outcome. We already know that Dr Clarke did not cover himself with glory, when he saw Cynthia.

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