Neurology. Charles H. Clarke

Shorvon

      National Hospital for Neurology & Neurosurgery, Queen Square, London

1 Neurology Worldwide : Public Health and Essential Neuro‐epidemiology

      The world over, one‐third of all serious illness is caused by brain disease and a tenth by other neurological conditions. I introduce here the epidemiology and burden of neurological illness. Public Health plays a minor role in neurology. It needs more attention.

Basic Data

      Incidence is new cases/100 000/year. Prevalence is the occurrence/1000 of the population, and lifetime prevalence the risk/1000 of acquiring a condition during life. These vary – between urban and rural settings and are linked to ethnicity, poverty, lifestyle/nutrition, vectors, war and sanitation. Data for specific age ranges are often more valuable than overall rates.

      In the United Kingdom:

       For stroke, incidence overall is 190/100 000/year, but those over 65, 1100/100 000/year.

       For Parkinson’s, incidence overall is 20/100 000/year and prevalence 2/1000. Over 65, incidence is 160/100 000/year and prevalence 10/1000.

       With epilepsy, the situation is shown in Figure 1.1.

A population’s age structure impacts heavily: there are more children and young adults in poor than in rich countries (Figure 1.2). Degenerative age‐related disease is increasing: the world’s population over 65 is to double between 2020 and 2030. Doubling time depends upon mortality rates, on the number of offspring per mother, and on cultural, financial and religious pressure. Examples are in Table 1.1.

Practical Neurology

Practical neurology is remarkably similar the world over – a neurologist in China, India or South America will be familiar with most conditions seen in Europe (Table 1.2). Variation between regions is determined largely by infections, such as malaria. Study of the full impact of Covid‐19 is unknown and not discussed here.

Figure 1.1 Standardized prevalence and incidence rates of treated epilepsy in a population of 2 052 922 persons in England and Wales in 1995. (Bars indicate 95% CI.) Prevalence of treated epilepsy: overall 5.15/1000 people (95% confidence interval [CI] 5.05–5.25).

      Source: Wallace et al. 1998.

Figure 1.2 Age structure in developed (Sweden) and developing (Costa Rica) countries.

      Source: Worldwatch Database, 1996, Worldwatch Institute.

      Causation

      The cause of a neurological disease is rarely simple. A condition is either:

      Genetic

       Huntington’s: a single gene disorder with high penetrance.

       Epilepsy: complex interactions between presumed susceptibility genes.

       Alzheimer’s: genetic influences in 10%, but not in the majority.

      Genetic and Environmental

       Parkinson’s disease: presumed genetic influences but susceptibility (curiously) reduced by smoking.Table 1.1 Population size and doubling times.Source: Data from The Population Reference Bureau, 2015CountryPopulation (millions)No. of births/motherDoubling time (years)Nigeria1076.223India9703.536China12361.867USA2682.0116Japan1261.5289UK601.7433Table 1.2 Incidence and point prevalence.Source: Data from various WHO sources; excludes shingles.DisorderIncidence (100 000/year)Point prevalence /100 000Migraine37012 100Acute stroke Subarachnoid haemorrhage TIA190 15 30900Epilepsy50710Dementia50250Parkinson’s disease20200Chronic polyneuropathies4024Bell’s palsy25Meningitis & infections15Brain tumours1010Trigeminal neuralgia41Multiple sclerosis Motor neurone disease4 290 4Muscular dystrophies16

       MS: genetic susceptibility and geographic location. MS is more common in latitudes around 50°N and S of the equator, and rare in the tropics (0°–23.5° N and S). Clusters of MS cases, for example on the W coast of Ireland.

      Evident and Preventable

       In traumatic brain injury, many severe brain injuries have been prevented by car seatbelts.

       Meningitis due to Haemophilus influenza, Streptococcus pneumoniae and Meningococci: immunisation.

      Generally, where primary causes are poorly understood, causation can be divided into

       predisposing factors (e.g. age, gender, genetic susceptibility)

       enabling factors (e.g. hypertension, poor nutrition, inadequate medical care)

       precipitating factors (e.g. exposure to infectious or noxious agent)

       reinforcing factors (e.g. repeated or prolonged exposure).

      Most neurological conditions are products of multifactorial influences, each of which alone would not cause the disease. It is thus helpful to study risk factors.

      Mortality, Life Expectancy and Quality of Life

      Mortality rate: the number dying of a condition divided by the number in the population.

      This information is of limited value without knowledge of the overall death rate.

      Life expectancy (median survival age) is often lowered in neurological disease, but data are complex.

      Taking epilepsy, one study followed over 500 cases for >10 years. The overall mortality ratio was 2.1. The hazard ratio (HR), or risk of death, for epilepsy overall, was 6.2. Life expectancy was reduced by some 2–10 years.

      Quality of Life

      It is not enough to prolong survival. In high grade gliomas, radiotherapy is known to prolong life by about six months. Side effects are severe; the trade‐off between survival and quality of life (QoL) is important. One study showed that how well a patient was before radiotherapy was a good indicator of disability‐free life after it. For those already disabled, radiotherapy offered little gain.

      Other Important Measures

       Birth rate: number of live births/mid‐year population;

       Fertility rate: number of live births/number