Generalidades de Argentina

3.1. Subjects

Subjects for the studies described in this thesis were recruited from the following sources:

3.1.1. The Specialist Cognitive Disorders Clinic

This clinic is based at the National Hospital for Neurology and Neurosurgery, Queen Square, London. This is a tertiary referral centre, and consequently these subjects tend to represent younger patients and those where there is more diagnostic uncertainty than a typical elderly population. The subjects recruited from the clinic included individuals with sporadic or familial AD, FTLD and other more unusual dementias. All subjects

underwent full clinical and neuropsychological assessment. Diagnosis was made

according to the criteria detailed in Appendix One.

3.1.2. Familial AD project

This is an ongoing longitudinal research project following individuals with a strong family history of histologically-proven AD. These families have, in many cases, subsequently been found to have mutations in the PS1 or APP genes. Affected individuals and asymptomatic family members at risk of developing the disease undergo annual assessments. These include a full history and neurological examination, MMSE, detailed neuropsychology and an MRI scan. This provides valuable information about presymptomatic individuals who subsequently go on to develop the disease, aiding in the understanding of the earliest signs of the disease. This cohort currently includes 30 affected and 48 at-risk individuals under follow-up with clinical and imaging assessments.

3.1.3. M1R1AD

The Minimum Interval Resonance Imaging in AD (MIRIAD) project aimed to determine the shortest interval required to detect volumetric change based on MRI, to

Subjects were assessed at baseline and at 2, 6, 14, 26, 38 and 52 weeks. At baseline all subjects underwent a full history, neurological examination, MMSE and detailed neuropsychology. Speed tests were performed at each visit and MMSE was repeated at 26 and 52 weeks. At 52 weeks the initial clinical diagnosis was reassessed and

neuropsychology was repeated. Apolipoprotein (APOE) genotyping and

electroencephalograms (EEG) were performed on patients alone. A volumetric MR scan was performed at each visit. At baseline, 6 weeks and 38 weeks two scans were acquired on the same day. In addition, MRS was performed at weeks 2, 26 and 52. A subset of these subjects (n=39) were assessed and scanned at 18 months, and at two years (n=22).

3.1.4. Normal controls

Neurologically healthy individuals with no family history of dementia are recruited to act as normal controls. These are largely recruited from spouses of affected or at-risk study members and a number of normal volunteers. All subjects have a detailed history taken and undergo a neurological examination, MMSE and a brief memory test, as well as MRI assessment. The spouses of study subjects are usually scanned on the same day as their partners and therefore have as closely comparable MR acquisitions as possible.

3.1.5. Pathologically-proven cases

As a result of being a patient at the Specialised Cognitive Disorders Clinic, a number of patients undergo brain biopsy to determine the cause of disease (see section 3.2). In addition to this, a number of patients followed through clinic have agreed to a post­ mortem to accurately diagnose the cause of dementia. Such cases are valuable as pathological evidence of disease is the “gold standard” of diagnosis. As a result, the scans obtained for clinical reasons, prior to death are a valuable resource for assessing group separation using different methodologies as there is diagnostic certainty. Some of these subjects were enrolled in other studies, such as MIRIAD. Seventy-nine subjects have had post-mortem confirmation of disease and at least one scan. Approximately half of these subjects have had a number of scans although these scans are of variable quality and some longitudinal imaging was performed on different scanners.

All subjects gave written informed consent for involvement in imaging studies and the Local Ethics Research Committee had given approval for all studies.

3.2. Clinical assessment

All subjects attending the Specialist Cognitive Disorders Clinic undergo comprehensive diagnostic evaluation. A full history, including family history, is taken together with a close informant. A full medical examination is performed as well as a neurological assessment. In addition, almost without exception, the following investigations are usually performed:

1. Detailed neuropsychology, in order to establish the nature and severity of any

cognitive deficits.

2. Standard screening blood tests to exclude other treatable causes of cognitive

problems such as impaired renal or liver function, B12 and thyroid function.

3. EEG to exclude seizures, or identify patterns indicative of a particular type of

dementia.

4. Neuroimaging will typically involve at least one MRI assessment. This can

exclude treatable causes such as tumours and subdural haematomas, or may indicate progressive neurodegeneration suggestive of some type of dementia pathology.

In the appropriate setting individuals may also undergo:

1. Genetic testing. In the case of individuals with a known genetic mutation in the

family, genetic testing may be offered to determine whether a subject is carrying the mutation. This is supported by a full genetic counselling service.

2. Lumbar puncture and CSF analysis. This investigation can be used to detect

inflammation due to e.g. meningitis or encephalitis, or to detect local CNS immune responses due to e.g. MS.

In a small number of subjects a brain biopsy may be performed. This is an invasive procedure which involves taking a small amount of brain tissue usually from the right (or non-dominant) frontal lobe. Definitive diagnosis can be obtained in this way by identifying a particular pathology. This technique is not used routinely, but may be suggested in the case of young individuals with dementia where it may be more likely

3.3. Imaging

3.3.1. Acquisition

All images were acquired on a 1.5T Signa MRI scanner (General Electric, Milwaukee, Wisconsin, USA) using a spoiled gradient echo technique. Scans generally included a sagittal T1-weighted scout sequence, an axial dual-echo sequence (T2-weighted and proton-density weighted) and a Tl-weighted volumetric image (124 contiguous 1.5mm slices). Imaging parameters varied according to the study, and details are given in Appendix Three.

3.3.2. Software and processing

Digitised images were transferred to a Sun workstation (Sun Microsystems Inc., Mountain View, CA) for analysis. Images which were judged on visual inspection to show a significant intensity gradient were corrected using the N3 correction algorithm (Sled et al., 1998) outlined in Chapter 2 (page 71).

3.3.2.1.MIDAS

The MIDAS (Medical Information Display and Analysis System) software (Freeborough et al., 1996a; Freeborough et al., 1997) runs on both Unix and Linux platforms and is implemented in the C programming language. This software allows simultaneous multiplanar display of 3D data. Brain structures can be outlined using both semi-automated and manual techniques. The whole brain segmentation tool within MIDAS is semi-automated and uses interactive thresholding, together with a series of erosions and dilations, to isolate brain tissue from other structures such as scalp and dura (see Figure 1.6 and Appendix Four).

Manual segmentation of brain sub-structures, such as the hippocampus, can be performed using a mouse-driven cursor. The simultaneous display of orthogonal views allows the operator to outline the structure in the coronal view whilst the segmentation is updated in real time in the sagittal or axial view. This aids in decisions about where boundaries should be defined (see Appendix Four). Both rigid-body, rigid-body plus scalings and shears, and fluid registration, as described in Chapter 2, can be implemented within the MIDAS software.

3.3.2.2.STATA

STATA (Stata Coporation, College Station, TX, USA) is a standard statistical package used for producing graphs and performing basic statistical analysis. This was used for the majority of statistical analysis and graph production within this thesis.

3.3.2.3.SAS

SAS (SAS Institute, Inc, Cary, NC, USA) was used for some statistical analysis as it allows complex models to be created where variances and covariances do not have to be similar.