Neurological thinking

Making a neurological diagnosis

There are two ways of making a neurological diagnosis clinically.

Pattern recognition or syndromic diagnosis

This is the only method in many neurological diagnoses where the site of the lesion cannot be deduced neuroanatomically, for example migraine, Parkinson’s disease, myotonic dystrophy and some forms of epilepsy. In addition, once experienced, pattern recognition can be used to work out the site of lesions, for example recognition of the clinical picture of Brown–Séquard syndrome (Fig. 2), which is due to a lesion of one-half of the spinal cord, rather than working out the localization from first principles (see p. 80 for more on Brown–Séquard syndrome).

Fig. 2 Brown-Séquard syndrome: a rightsided T8 lesion.

Different levels of diagnosis

It is important to understand that neurological diagnoses can be made with different degrees of sophistication (Fig. 3; Box 1). For example, it can be deduced that a right-handed patient with a slowly progressive right-sided hemiparesis and aphasia has a left hemisphere lesion (anatomical diagnosis) and that it is likely to be a space-occupying lesion because of the slow onset (clinical diagnosis). A brain scan demonstrates a mass that is thought to be an intrinsic brain tumour (radiological diagnosis), and biopsy and neuropathological examination find an astrocytoma (pathological diagnosis).

Fig. 3 Different levels of diagnosis.

Box 1 Different types of diagnosis

Anatomical

Aetiological

Syndromic

Pathological

Radiological

Genetic

Following a clinical examination there may well not be a definitive diagnosis, but there should be a working diagnosis, usually with a differential diagnosis. This could be a definitive syndromic diagnosis (e.g. migraine with aura, clinically definite multiple sclerosis), a syndromic diagnosis requiring further investigation (e.g. motor neurone disease), an anatomical diagnosis (e.g. myopathy), a description of the clinical problem (e.g. single seizure or left sixth nerve palsy) or simply a description of the symptom (e.g. blackout ?cause).

Common and important disorders

In considering any clinical problem it is useful to think about the common disorders, as these occur most commonly. However, in most clinical situations there are rare but important disorders that need to be considered much more often than their incidence merits. For example:

Wilson’s disease is a rare abnormality of copper metabolism that can present with Parkinsonism. Drug therapy to prevent further accumulation of copper is the specific treatment. This is rare but needs to be considered in younger patients with movement disorders.

Migraine and tension headache are common. Temporal arteritis, subarachnoid haemorrhage and meningitis are rarer, but are life-threatening and require specific treatments and therefore need to be considered frequently despite occurring rarely.

Throughout this book, estimates of the incidence of the conditions discussed will be given. This is important information in reaching a diagnosis. The example often given to illustrate this is in the identification of a small bird outside a window. It is much more likely to be a sparrow than a canary. However, this is not a good illustration as canaries are bright yellow and if it was bright yellow it probably is a canary. A better example is a bird of prey circling above; it is a buzzard, but what type? A bird book tells you there are three European buzzards (the common buzzard, rough-legged buzzard and the honey buzzard) that differ in minor ways but also that the common buzzard is common, whereas the rough-legged and honey buzzards are rare visitors to the UK. It is almost certainly a common buzzard, but one should watch out for the differences in wing length and width that distinguish these other buzzards.

Investigation

The next stage is planning the investigation. This depends on the condition concerned. Investigations are used in four ways:

In undertaking these investigations it is important to be aware of the sensitivity (how often does the test find true positives?) and specificity (reflecting false positives) of the different investigations in different clinical settings. Accurate clinical assessment enables the best use of investigations.

Neurological thinking

Clinical assessment involves the synthesis of information obtained using clinical skills, history taking and neurological examination, combined with background knowledge about neurological disease.

Diagnoses can be made at different levels, for example syndromic, radiological or pathological.

Common disorders are important because they are common. For different clinical problems there are a few rare but important conditions to consider.