How To Scan For Dementia

Transcription

1 Yorkshire and the Humber SCN Guidance on Neuro-imaging in Dementia January 2015 (Review date January 2017)

2 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) 1 states: 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.

3 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 centres 3. 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 prerequisites 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."

4 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 DaTSCAN TM PET

5 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 Coronal CT 3 O 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: McKeith 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: