The background of FDG-PET
FDG-PET is a highly useful imaging modality for the diagnosis of uncertain or difficult to diagnose primary neurodegenerative disorders.
Patterns of altered cerebral glucose metabolism seen at FDG-PET are useful as imaging biomarkers to assist in making the clinical diagnosis of neurodegenerative diseases causing dementia.
- NICE Guidelines for Dementia 2018 recommend:
- If diagnosis is uncertain and AD is suspected, consider FDG-PET (or perfusion SPECT if FDG-PET is unavailable) or examining CSF.
- If the diagnosis is uncertain and FTD is suspected consider FDG-PET (or perfusion SPECT if FDG-PET is unavailable).
- Do not rule out dementia solely on normal imaging.
- In 2016 the Royal College of Physicians and Royal College of Radiologists published Evidence-based Indications for the use of PET-CT in the UK (The Royal College of Radiologists, 2016). The guidance comprises an up-to-date summary of relevant indications for the use of PET-CT where there is good evidence that patients will benefit from improved outcomes.
- They recommend FDG PET-CT be used in the evaluation of memory loss/neurological signs suggestive of dementia and differentiation of types of dementia in selected patients and confirmed that FDG PET -CT can be used as a pathophysiological biomarker of AD by depicting reduced FDG uptake in the brain.
- In 2016 H. Motara et al conducted a study to evaluate the clinical impact of FDG PET brain imaging in patients with cognitive impairment, who did not have a clear diagnosis after initial expert assessment and standard neuro radiological examinations in a routine clinical setting.
- The study also aimed to assess the accuracy, sensitivity, and specificity of FDG PET/CT in diagnosing the commonest cause of neurodegenerative dementia, i.e. AD, when compared with the final clinical diagnosis, in patients presenting with difficult to diagnose dementia at a single tertiary referral centre in the UK.
- Their findings were that FDG PET/CT brain imaging has a significant clinical impact when performed selectively in patients with cognitive impairment and shows high accuracy in the diagnosis of AD in “real-world” clinical practice. The study showed that in a routine clinical PET/CT service in the UK, FDG PET/CT led to a change in the pre-test clinical diagnosis in 35% of cases, obviated the need for further investigations in 42%, led to a change in therapy in 32%, and overall, had an impact on clinical management in 81%, thereby indicating the substantial clinical utility of FDG imaging in selected patients with difficult to diagnose dementia.
In 2020 The Royal College of Psychiatrists working with ARUK undertook an online survey and series of focus groups to understand Old Age Psychiatrists’ views on diagnosing and treating Alzheimer’s disease before dementia.
The online survey was completed by 493 members of the Old Age Psychiatry Faculty, Royal College of Psychiatrists (Dec 2019/Jan 2020) and 8 focus groups (42 clinicians, Oct 2020) from across the UK.
The results were highlighted in Are we ready to deliver disease-modifying treatments, a report from Alzheimer’s Research UK and the Royal College of Psychiatrists published in May 2021. Findings include:
- that specialists are keen to embrace the arrival of new dementia drug treatments but need much more support in order to effectively implement them into their clinical practices.
- 36% of psychiatrists thought their services could adapt to deliver disease-modifying treatments within a year
- 6% of psychiatry services are able to fully meet the NICE guidelines regarding accessing further biomarker and diagnostic tests for Alzheimer’s disease.
Implementing FDG-PET into a health board service
A pilot project was established by ABUHB in late 2019. The project aimed to benefit patients in the Gwent area; increasing earlier diagnosis and diagnostic rates for dementia, achieving more reliable diagnosis of dementia subtype, enabling earlier disease-specific treatment and access to psychosocial support and reduction of carer burden.
The project was also developed with a view to scaling to a national offer should it generate positive outcomes.
- Patient and carer idea
- Working with ABUHB Older Adult Mental Health Directorate, ABUHB Radiology Directorate in partnership with Wales Research and Diagnostic Positron Emission Tomography Imaging Centre (PETIC) and Royal College of Psychiatrists in Wales
- Gwent Regional Partnership Board commissioned independent review of Dementia Services 2019 identified commissioning priorities, included priority around improved diagnostic pathway and rate by widening access to diagnosis
- ICF Project cost £100,269, (60FDG PET scans and 20 Amyloid PET scans)
- Targeted at patients in Memory Assessment Services in ABUHB for whom the standard memory assessment pathway does not clarify diagnosis.
- Trained psychiatrists, neurologists and geriatricians around the neuroimaging needed for diagnosis of early or uncertain dementia
- Developed operational policy
- Benefit to patients in Gwent area; increase earlier diagnosis and increase diagnostic rate for dementia, achieve more reliable diagnosis of dementia subtype, enable earlier disease specific treatment and access to psychosocial support and reduce carer burden
In recognition of the need to improve diagnosis, strategic clinical networks (SCNs) in the UK have produced specific guidance (Burn W Chowdury F, 2015) on the use of conventional and highly specialised neuroimaging in dementia, which defines the role of FDG PET/CT by judiciously limiting its use to clinical scenarios in the context of cognitive impairment as indicated below:
- Diagnostic difficulty after history, clinical assessment, structural imaging, and formal cognitive testing
- Early-onset dementia (<65 years)
- Clinical uncertainty about subtyping of dementia, especially differentiating AD and FTD
- Atypical presentation of AD or FTD
- Multiple established psychiatric co-morbidities (depression, schizophrenia, bipolar illness, alcohol-related, learning difficulties) with co-existing and/or new-onset cognitive impairment
- Inconclusive formal neuropsychological assessment
We have evaluated the clinical impact of FDG PET-CT brain imaging in patients with cognitive impairment across 6 memory services in ABUHB.
- Funding was obtained to undertake sixty FDG PET-CT scans during the pilot period.
- 52 FDG PET-CT scans were completed by September 2020.
- Feedback for analysis from referring Consultants has been received for 23 patients.
- FDG PET-CT brain imaging has a significant clinical impact when performed selectively in patients with cognitive impairment and shows high accuracy in the diagnosis of AD in real-world clinical practice in Wales.
- Change in the pre-test clinical diagnosis: 61%
- Increased confidence in their diagnosis: 100%. This finding compares favourably with the results obtained by R Ossenkoppele et al (R Ossenkoppele, 2013) which showed that PET results led to a change in diagnosis in 23% of patients. Diagnostic confidence increased from 71 (+/- 17)% to 87 (+/-16)% after PET (P < 0.001).
- In the ABUHB pilot study patients were selected rigorously to include those with the most diagnostic uncertainty which may have contributed to the high percentage with change in clinical diagnosis as well as the 100% increased confidence in diagnosis.
- Further investigations cancelled: 91%
- neuropsychology testing: 52%
- watchful waiting and associated repeat ACEIII: 43%
- other speciality appointments: 8.3%
- 91% of the patients had their therapy changed:
- commencement of antidementia medication: 52%
- discontinuing or avoiding of antidementia medication: 35%
- proposed Electroconvulsive Therapy was cancelled: 13%.
- compares favourably with a previous study by A Elias et al (A Elias, 2014) which showed changed prescription of antidementia medication in 17% of patients.
- Overall clinical management was changed in 91% of cases, this demonstrates the huge clinical utility of FDG PET-CT imaging in selected patients with difficult to diagnose dementia.
A national approach to FDG-PET in Wales
Following the pilot project the Welsh Health Specialised Services Committee has commissioned FDG-PET scans for dementia nationally.
ABUHB have committed to a number of actions in continuing work into developing and enhancing the infrastructure for early and effective diagnosis of dementia. This includes:
- continuing to provide access to access to Amyloid PET scans in ABUHB for patients with suspected dementia where the diagnosis is uncertain
- piloting a CSF analysis pathway to aid diagnosis of dementia in ABUHB.
- Health Boards have identified clinical leads who will hold responsibility within their MDT for referral for FDG-PET.
- In partnership with PETIC, The Royal College of Psychiatrists Wales has held a workshop with clinical leads across Wales to highlight the project and clinical pathway.
- A regular schedule of meetings is being established with clinical leads across Wales to discuss progress in embedding FDG-PET, this is in partnership with colleagues in radiology.
- The Royal College of Psychiatrists will be further holding a conference on the 17th September 'Brain health and effective, early diagnosis of dementia'.