Yorkshire and the Humber SCN Guidance

on Neuro-imaging in Dementia

January 2015 (Review date January 2017)

Introduction

This guidance has been written by the Yorkshire and Humber Strategic Clinical Network for

Dementia working group which included old age psychiatrists, physicians, radiologists and a

GP.

The purpose of this guidance is to advise clinicians in primary and secondary care on the

role of neuro-imaging in the assessment of dementia. It addresses the questions of when

neuro-imaging should be undertaken and which scan should be requested. It also

emphasises the importance of providing detailed information on request forms to obtain the

best reports.

When to Scan

Nice Clinical Guideline (CG42)1states:

“Structural imaging should be used in the assessment of people with suspected dementia to

exclude other cerebral pathologies and to help establish the subtype diagnosis”. “Imaging

may not always be needed in those presenting with moderate to severe dementia, if the

diagnosis is already clear”.

Neuro-imaging should be used in the assessment of most people with suspected dementia

to:

1. Exclude other pathologies which may present with symptoms similar to dementia eg

cerebral tumours, sub-dural haematomas and hydrocephalus

2. Establish the sub-type (cause) of dementia eg Vascular Dementia, Alzheimer’s

Disease etc

However scanning is unnecessary for people with severe dementia or who are very frail and

dependent when it is unlikely that the results of a scan would influence management.

There may be other situations where a clinician has to evaluate the benefit of scanning, for

example local geography and the distance a patient has to travel to obtain a scan and the

associated distress and inconvenience this may cause.

It must be remembered that a scan does not in itself diagnose dementia it provides support

for the clinical diagnosis and can help establish the sub-type (cause).

Which Scan

Nice guidelines state “Magnetic resonance imaging (MRI) is the preferred modality to assist

with early diagnosis and detect sub-cortical vascular changes, although computed

tomography (CT) scanning could be used.”1

However in practice MRI can be poorly tolerated by some older patients and those with late

stage dementia. MRI studies take 25 minutes to perform and the patient has to lie perfectly

still in a tunnel with their head restricted within a helmet (the MRI coil). The scan produces

an extremely loud noise which can be frightening and disorientating for the patient.

In contrast CT scans are quick to perform (1-2 minutes) and the vast majority of patients

tolerate it well. CT is also significantly cheaper than MRI. A volumetric CT should be

performed as it can be reconstructed into a coronal plane and has been shown to be as

good as MR for quantifying medial temporal lobe volume and detecting atrophy (which

occurs in Alzheimer’s disease)2.

However MRI scans do have a place in the assessment of people with dementia, particularly

for those with unusual or atypical presentations and acute or rapidly progressive dementia.

As in these situations MRI is better at identifying subtle vascular changes and detecting rarer

conditions such as multiple sclerosis, progressive supra-nuclear palsy, cortico-basilar

degeneration, prion diseases and limbic encephalitis. Also MRI may be better at detecting

atrophy in the posterior parietal regions in patients suspected of having younger onset

Alzheimer’s disease.

Functional Imaging

Functional neuro-imaging using nuclear medicine techniques is generally reserved for the

relatively small number of patients with dementia which is difficult to diagnose or of early

onset when the knowledge and subtype of dementia will influence management.

Techniques available include positron emission tomography (PET) with fluoro-deoxyglucose

(FDG) and amyloid plaque tracers and single photon emission computed tomography

(SPECT) with perfusion tracers e.g. HMPAO. PET imaging is recognised as having

increased accuracy over SPECT imaging in dementia but is generally only available in

tertiary centres3. Functional imaging of dopaminergic neurones with DaTSCAN™ can assist

in the diagnosis of dementia with Lewy bodies (DLB)4.

Given the relative cost, functional imaging should be reserved for situations where the

precise diagnosis is crucial and the information obtained would alter management eg early

onset or atypical presentations of dementia usually in younger patients. Certain pre-

requisites must be fulfilled for patients to have these scans in particular co-operability (as

scanning takes time) and urinary continence (as radioactive isotopes are used). More

information can be obtained from hospital departments of nuclear medicine.

Scan Requests

Scan reports are very dependent on the information provided by the requesting clinician. Key

details about the patient should include: age, duration of memory problems, symptom

progression, presence or absence of vascular disease (cerebral, coronary and peripheral)

and associated neurological symptoms. The requesting clinician should also seek specific

clarification on the presence of medial temporal lobe (hippocampal atrophy), significant

vascular ischaemic change and the presence of other intracranial pathology such as

tumours.

An example request:

"80 year old with 3 year history of short term memory difficulties. Vascular risk factors

include history of hypertension. Need to clarify the presence of significant vascular

ischaemic changes, medial temporal lobe atrophy (hippocampal atrophy) or space

occupying lesion."

Scan Reports

To maximise the diagnostic value of the scan it is important that the imaging is interpreted by

a radiologist experienced in the field. This is particularly true of MRI studies as their

interpretation can be difficult.

Useful comments in a scan report of a patient suspected of having dementia would be the

presence or absence of:

1. Vascular changes

Some form of quantification of cerebrovascular disease is helpful. This should include the

presence of lacunar infarcts, established cortical infarcts and small vessel disease that is

disproportionate for age.

2. Early parietal lobe and medial temporal lobe (hippocampal) atrophy

These are known bio-markers of Alzheimer’s disease

3. Any evidence of disproportionate atrophy affecting other areas of the brain eg frontal

lobes

These may suggest dementia of other subtypes eg fronto-temporal dementia

4. The presence (or absence) of other intracranial pathology and its likely significance

Incidental pathology is often discovered on CT scans in particular meningiomas. These are

usually benign and asymptomatic. They generally require no treatment other than periodic

monitoring but it is important to clarify the local protocol for referring such tumours to the

neurosurgeons. An urgent specialist opinion is warranted if they are large, show

compressive features or if there is associated cerebral oedema.

Costs

Scan costs vary between centres and are influenced by local factors and commissioning

arrangements. The costs quoted are for illustrative purposes only.

CT £75

MRI £150

SPECT £350-500

DaTSCANTM £850-950

PET £750-1000

Members of the SCN Working Group

Dr Wendy Burn, Consultant in Old Age Psychiatry, Leeds and Joint Clinical Lead, Yorkshire

and Humber SCN for Dementia

Dr Fahmid Chowdhury, Consultant in Radiology and Nuclear Medicine, Leeds

Dr Oliver Corrado, Consultant Geriatrician, Leeds and Joint Clinical Lead, Yorkshire and

Humber SCN for Dementia

Dr Ian Craven, Consultant Neuroradiologist, Leeds

Dr Rob Ghosh, Consultant Geriatrician, Sheffield

Dr Kirsty Harkness, Consultant Neurologist, Sheffield

Dr Dan Harman, Consultant Geriatrician, Hull

Dr Sara Humphrey, General Practitioner, Bradford and GP Adviser, Yorkshire and Humber

SCN for Dementia

Penny Kirk, Quality Improvement Manager (Dementia), Yorkshire and Humber Strategic

Clinical Networks

Dr Tolulope Olusoga, Consultant Psychiatrist and Senior Clinical Director, Tees, Esk and

Wear Valleys NHS Foundation Trust

Acknowledgements

We thank the South West Strategic Clinical Network for sharing their guidance and inspiring

us to produce something similar

References

1 National Institute for Health and Care Excellence Clinical Guideline 42 (CG42) “Dementia:

Supporting people with dementia and their carers in health and social care” November 2006

2 Coronal CT

3O’Brien JT, Firbank MJ, Davison C, et al. 18F-FDG PET and perfusion SPECT in the

diagnosis of Alzheimer and Lewy body dementias. J Nucl Med 2014; 55:1959-1965

4McKeith I, O’Brien J, Walker Z, et al. Sensitivity and specificity of dopamine transporter

imaging with 123I-FP-CIT SPECT in dementia with Lewy bodies: a phase III, multicentre

study. Lancet Oncol 2007; 6:305-313.