Sian is a 15-year-old girl, referred to paediatric outpatients by her GP. The letter says, ‘Thank you for seeing this girl who has had her first fit.’ Three weeks ago she was at school when the fire alarm went off unexpectedly. She felt faint and clammy. Friends tried to help her to walk out of the classroom, but after about a minute she collapsed to the floor and had a brief episode of jerking movements affecting all four limbs. There was no incontinence or tongue biting. She regained consciousness within a minute but continued to feel weak for a few hours afterwards. Sian had a febrile convulsion at 18 months of age and she has fainted on about five occasions, mostly in emotional situations or when it has been hot. She describes herself as an anxious girl, and has a sensation of her heart racing every few weeks. She has never been in hospital, but has seen her GP for heavy periods. There is no family history of epilepsy, but her aunt collapsed and died at the age of 28 in Canada. She is top of her year at school and hopes to be a doctor or lawyer.
Examination
Her height is 170 cm (91st centile) and her weight is 53kg (50 th). Cardiovascular, respiratory, abdominal and neurological examinations are normal.
Questions
• What are the possible causes of her collapse?
• What is the most important investigation to perform at this stage?
Medicine
Causes of a funny turn
Distinguishing features in the history
Epileptic seizure Aura, incontinence, tongue biting, family history
Cardiac arrhythmia Palpitations, sudden collapse, exercise-related
Neurally mediated syncope Preceding stimulus, dizziness, nausea
Panic attack Hyperventilation, paraesthesia, carpopedal spasm
Breath-holding attack Usually a toddler, upset/crying
Reflex anoxic seizure Usually infant/toddler, painful stimulus
Pseudoseizures Psychological problems
Other causes
Hypoglycaemia
Other metabolic
derangements
Drugs, alcohol
In this case, the history is most suggestive of a neurally mediated (vasovagal) syncope, a cardiac arrhythmia or perhaps a panic attack. The history is less typical of an epileptic seizure, and the most likely reason for the brief convulsion is hypoperfusion of the brain due to low blood pressure while her friends held her upright – an anoxic seizure. This terminated quickly when she was supine after collapsing. The single most important investigation is an ECG, as this may show a potentially lifethreatening cardiac cause. An EEG is generally not performed after a first seizure because it may be normal in those who go on to have epilepsy and abnormal in those who never have another seizure, with the EEG adding little to prognosis at this stage. Blood tests are often performed for glucose, electrolytes, calcium and magnesium, but are frequently unhelpful. Sian’s ECG is shown in Figure 13.1.
Her ECG shows a prolonged corrected QT interval, making the diagnosis of a long QT syndrome. This disorder has a number of genetic causes, and in some cases an arrhythmia can be precipitated by a sudden loud noise. This girl went on to require anti-arrhythmic drug treatment and an implantable cardiodefibrillator. The QT interval is measured from the start of the QRS complex to the end of the T-wave; the QT interval is corrected (QTc) for heart rate by: QTc QT/(R – R interval). QTc is normally around 0.41 s and should be less than 0.45 s. In this case it is 0.52 s.
KEY POINTS
• The commonest cause of fainting in a teenager is neurally mediated (vasovagal) syncope.
• Cardiac causes should always be considered in the differential of epilepsy and funny turns.
• An ECG is almost always indicated.
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