Population Surveys Scopes, Prevalence, Incidence, Health Registries

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Population SurveysScopes, Prevalence, Incidence,
Health Registries

• Ettore Beghi
• Institute for Pharmacological Research Mario
  Negri, Milano, Italy

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SCOPE OF POPULATION SURVEYS

• Measure prevalence
• Measure incidence
• Measure mortality
• Identify cases for case-control studies
• Identify exposures for cohort studies
• Study familial aggregation/genetics
• Screen candidates for prevention/early treatment

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ANATOMY OF A POPULATION SURVEY

• Definition of the study population
• Definition of disease
• Case ascertainment (prevalence, incidence and
  mortality)
• Calculation of epidemiological indexes
• Distribution by time, place person

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DIAGRAM OF THE IDENTIFICATION OF A DISEASE IN THE
GENERAL POPULATION
Kurtzke, 1978
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HOW TO DEFINE A POPULATION

• Geographic boundaries - Residency -
  Istituzionalization - Migration
• Temporal boundaries - Prevalence period
  (point, period, lifetime) - Incidence period

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MEASURES OF DISEASE FREQUENCY

• INCIDENCE Number of individuals in a population
  that become ill in a stated period of time
• CUMULATIVE INCIDENCE Proportion of a fixed
  population that becomes ill in a stated period of
  time
• PREVALENCE Proportion of a population affected
  by a disease at a given point of time
• MORTALITY Number of individuals in a population
  died for a disease in a stated period of time

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PREVALENCE AND INCIDENCE
Prevalence Incidence x average duration
Incidence
Migrating in
Migrating out
Prevalence
Death
Recovery
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SOURCES OF NEUROLOGICAL DISEASES IN
EPIDEMIOLOGICAL STUDIES

• Hospital records
• Ambulatory records
• Electrophysiological (EMG) records
• General practitioners files
• Disability records
• Lay associations
• Tertiary centers
• Death certificates
• Diagnosis related groups (DRGs)
• Disease registries

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MIGRAINE IS A HETEROGENEOUS AND ILL-DEFINED
CLINICAL CONDITION

• Intensity, duration, frequency and
  characteristics of attacks tend to vary in the
  general population
• In each patient, symptoms may vary with time
• Many individuals may have different types of
  headache
• Many individuals do not consult their doctor for
  headache

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MIGRAINE WITHOUT AURA (IHS, 1988)

• A. At least 5 attacks with criteria B-D
• B. Attacks lasting 4-72 hr (no or poor treatment)
• C. Headache with at least two features -
  Unilateral - Pulsating - Moderate
  or severe
• D. At least one among - Nausea and/or
  vomiting - Photophobia and/or phonophobia
• E. At least one of the following - Other
  disturbances excluded by hx and examination -
  Other disturbances excluded by diagnostic
  tests - Other disturbances, but migraine attacks
  verified

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CHANGE IN THE PREVALENCE OF MIGRAINE WHEN VARYING
THE NUMBER OF IHS DIAGNOSTIC CRITERIA
Merikangas et al, 1990
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EPILEPSY AND EPILEPTIC SEIZURES

• EPILEPSY Clinical condition characterized by
  repeated unprovoked seizures
• UNPROVOKED SEIZURE Seizure occurring in the
  absence of known precipitants it may occur at
  the presence of a non-recent CNS injury
• ACUTE SYMPTOMATIC SEIZURE Seizure occurring in
  close temporal relationship with an acute CNS
  insult

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EPILEPSY, ACTIVE IN REMISSIONDefinitions

• ACTIVE EPILEPSY epilepsy currently being treated
  or whose most recent seizure has occurred
  (usually) within the past two to five years
  (Thurman et al, Epilepsia, 2011)
• EPILEPSY IN TERMINAL REMISSION absence of
  seizures for 2 or 5 years without AEDs

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ACUTE SYMPTOMATIC SEIZURESInterval from
precipitating factor
CNS Insult Timing of occurrence
Stroke, head trauma, cerebral anoxia 1 week
Cerebral infection Positive clinical/laboratory findings
Brain abscess, cerebral tuberculoma During treatment
HIV infection Acute infection/metabolic disturb
Arterovenous malformation Acute hemorrhage
Multiple sclerosis Within 7 days of relapse
Autoimmune diseases Symptoms/signs of activation
Neurodegenerative disorders None identified
Epidemiology Task Force, Epilepsia 2009
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EPIDEMIOLOGICAL INDEXES OF EPILEPSY IN
INDUSTRIALIZED COUNTRIES

• Incidence Epilepsy 29-53 100,000/yr
  Epilepsysingle seizures 73-86 Acute sympt
  seizures 20-30 Status epilepticus 10-40
• Cumulative incidence 1-3
• Prevalence Active epilepsy 5-8
  x1,000 Lifetime 15-50
• Mortality 1-4 x100,000/yr
• SMR 2-3

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DeCarli, Lancet Neurol 2003 215
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PREVALENCE OF COGNITIVE IMPAIRMENT ACCORDING TO
CLINICAL DEFINITION
DeCarli, Lancet Neurol 2003 215
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PROBLEMS REGARDING THE DIAGNOSIS OF POLYNEUROPATHY

• The majority of the available data comes from
  clinical series
• The diagnosis of polyneuropathy is based on
  clinical and elettrophysiological features
• Polyneuropathy includes a wide spectrum of
  disorders ranging from symptomatic clinical
  conditions to subclinical variants
• Diagnosis should be confirmed by a neurologist

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Polyneuropathy in the ElderlyPrincipal Symptoms

• Muscle cramps
• Restless legs syndrome
• Burning feet
• Muscle pain
• Problems with handling objects
• Impairment of standing and gait
• Glove and stocking paresthesiae

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POLYNEUROPATHY IN THE ELDERLYValidity of the
screening questions
Monticelli et al, Neuroepidemiology 1993
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POLYNEUROPATHY IN THE ELDERLYInter-rater
agreement (kappa statistic)
Monticelli et al, Neuroepidemiology 1993
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EL ESCORIAL CRITERIA FOR THE DIAGNOSIS OF ALS

• Based on the topographical location of upper
  (UMN) and lower motor neuron (LMN) signs in 4 CNS
  regions, progression of these signs, and absence
  of other diseases
• Degree of diagnostic certainty (definite,
  probable, possible, suspected ALS) based on a
  different combination of UMN and LMN signs

Brooks, 1994
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EL ESCORIAL CRITERIA FOR THE DIAGNOSIS OF ALS

• DEFINITE ALS - LMN and UMN signs in 3
  spinal regions - LMN and UMN signs in the
  bulbar region and in 2 spinal regions
• PROBABLE ALS - LMN and UMN signs in 2
  spinal regions
• POSSIBLE ALS - LMN and UMN signs in 1
  region - UMN signs in 2 or more regions -
  LMN signs rostral to UMN signs
• SUSPECTED ALS - LMN signs in 2 or more
  regions

Source J Neurol Sci 1994 124 (suppl) 96-107
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DISEASE REGISTRIES

• Lists of diseases (or disease groups) in
  well-defined populations
• Collection of data on disease burden and
  identification of patients cohorts to be
  followed for specific purposes
• For rare diseases, registries represent a
  (re)source for the collection of sizable numbers
  of cases for focused studies

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EXPLANATIONS FOR HIGHER AND MORE HOMOGENEOUS
RATES IN EUROPEAN REGISTRIES

• Prospective inception of cases
• Multiple sources
• Fairly complete case ascertainment
• Continuous surveillance
• Use of the same diagnostic criteria

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OBJECTIVES OF A POPULATION-BASED REGISTRY

• Incidence and prevalence of the target condition
• Temporal and geographic trends of the disease
• Full clinical spectrum of the disease
• Clinical and paraclinical markers of the disease
• Practical management and socio-economic
  implications of the disease
• Data banks for clinical/biological material

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PREREQUISITES FOR THE START OF A REGISTRY

• Definition of the population at risk
• Selection of the best source(s) of cases
• Choice of the correct diagnostic criteria

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SOURCES OF CASES

• Hospital records
• Outpatient records
• Neurophysiology units archives
• General practitioners files
• Disability records
• Lay associations files
• ALS centers
• Death certificates
• Administrative files (hospital discharge
  diagnoses)

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THE EURALS CONSORTIUM

• Ireland 5.0M
• Scotland 5.0M
• Lancashire Cumbria 1.8M
• London 2.8M
• Italy (all) 8.0M
• Belgrade 2.0M
• Madrid 1.0M
• Limousin 0.7M
• Germany ?
• Russia ?
• Israel ?
• Total gt25M

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PRACTICAL RECOMMENDATIONS TO START A
POPULATION-BASED REGISTRY

• Select a well-defined geographic area
• Identify one or more accessible sources
• Use valid and reliable diagnostic criteria
• Set a network of specialists able to trace all
  cases residing in the area
• Select a number of core variables to verify the
  correctness of the diagnosis and define the
  general profile of the disease
• Start specific studies only after preparing
  ad-hoc protocols and case collection forms