Dementia Research Group MRI, rates of atrophy and Alzheimer’s disease Nick Fox Dementia Research Group Institute of Neurology, UCL Queen Square, London England

Is it reasonably likely that a change in atrophy rate would predict clinical outcome in AD?

Atrophy rates and AD: overview The relationship of atrophy rates to pathological and clinical progression in untreated patientsThe relationship of atrophy rates to pathological and clinical progression in untreated patients Disease modification vs. symptomatic effect?Disease modification vs. symptomatic effect? Is it reasonably likely that atrophy rate changes would predict clinical benefit in treated patients?Is it reasonably likely that atrophy rate changes would predict clinical benefit in treated patients? How might atrophy rates be uncoupled from clinical benefit? Can this be protected against?How might atrophy rates be uncoupled from clinical benefit? Can this be protected against?

AD is characterised pathologically by neurofibrillary tangles, neuritic amyloid plaques, synapse loss, dendritic pruning,cell loss and atrophy… MRI can visualise and measure atrophy rates

Time 0 18months36months H Serial coronal MRI of an individual with initially mild AD

MCI Scan 1

MCI Scan 2

AD Scan 1

AD Scan 2 6 months later

Controls AD Rate of brain volume loss %/yr 2.8% (+/-1) 0.2% (+/-0.3)

Reproducibility Scan-rescan (a real test of reproducibility)Scan-rescan (a real test of reproducibility) Acquire a single scan and then two further scans on the same day one year laterAcquire a single scan and then two further scans on the same day one year later Scan A Scan C Scan B BBSI AB BBSI AC

y = 1.00x R > First measure / cc Repeat measure / cc RMS Error = 1.6 cc

y = 0.48x R = Fall in MMSE % LOSS OF BRAIN VOLUME Cognitive decline in AD correlates with rate of cerebral atrophy Fox et al Neurology 1999;52:1687-9

At risk F206 (well) Brain volume vs. time Days from first scan %

AD: brain volume vs. time Days from first scan %

Rate of atrophy predicts conversion to AD in at-risk subjects Fox et al The Lancet 1999; 353:2125

/97 11/97 AD: At risk subject - serial scans registered to 1993 baseline

93 11/97 Red = loss

% Time since first scan (days) Brain Volume as percentage of TIV symptomssymptoms Normal range: 95%CI

Normal control range Symptom onset Fulfils clinical criteria for AD Scahill et al PNAS 2001

Cerebral atrophy rates on MRI and clinical progression in AD Atrophy progression in untreated ADAtrophy progression in untreated AD –Is inexorable –And correlates with cell loss MR-based measures are reliable and sensitive to change at a clinically meaningful levelMR-based measures are reliable and sensitive to change at a clinically meaningful level Rates of cerebral atrophy on MRRates of cerebral atrophy on MR –Are increased in AD –Predict conversion to AD –Correlate with cognitive decline –Biologically plausible: regional specific atrophy reflects pathological and clinical progression

Differentiating Disease Slowing From Symptomatic Benefit Is benefit sustained?Is benefit sustained? Are all disease effects modified?Are all disease effects modified? Disease modifying effects take place nearer the causal end of the processDisease modifying effects take place nearer the causal end of the process Disease process Disease effects Clinical outcomes

Dementia Research Group “a surrogate … should capture the full effects… …on the clinical outcome” Can change in one happen without change in the other?Can change in one happen without change in the other? Are changes correlated?Are changes correlated? Clinically meaningful?Clinically meaningful? Are measures sensitive?Are measures sensitive? Feasible?Feasible?

Neuronal degeneration is closely linked to progression of cognitive decline Pathological process Cell loss Cognitive decline and death Synapse loss Destruction of neuronal networks

Could volume change occur without neuronal loss in AD? Neurones Other cells Water Protein Yes – neuronal loss is not the sole determinate of cerebral volume – e.g. inflammation, hydration, osmotic effects… 3% cerebral volume change after haemodialysis Walters, Fox et al Nephron 2001;87:143-7

Atrophy and progression Neuronal changes are neither necessary nor sufficient to produce volume changesNeuronal changes are neither necessary nor sufficient to produce volume changes However progressive volume loss is more likely to be related to progression in neuronal lossHowever progressive volume loss is more likely to be related to progression in neuronal loss >2 imaging time points>2 imaging time points Including off treatmentIncluding off treatment %

Dementia Research Group It is reasonably likely that A measure of slowed neuronal loss would predict clinical outcome and that slowing would constitute disease modificationA measure of slowed neuronal loss would predict clinical outcome and that slowing would constitute disease modification A slowed rate of neuronal loss would result in reduced atrophy ratesA slowed rate of neuronal loss would result in reduced atrophy rates If the reduction in atrophy rate followed the region- and time-related pattern of the pathology then it would be reasonable to conclude that clinical outcome would also be improvedIf the reduction in atrophy rate followed the region- and time-related pattern of the pathology then it would be reasonable to conclude that clinical outcome would also be improved

Dementia Research Group Summary Atrophy rates correlate with and predict progression in untreated patientsAtrophy rates correlate with and predict progression in untreated patients The causality of the link between neurodegeneration and atrophy is plausibleThe causality of the link between neurodegeneration and atrophy is plausible It may be reasonable, with appropriate study designs, to suggest changes in rate of atrophy are due to reduced neuronal degeneration and are likely to predict clinical benefitIt may be reasonable, with appropriate study designs, to suggest changes in rate of atrophy are due to reduced neuronal degeneration and are likely to predict clinical benefit Inevitably disease modifying drug(s) are required to strengthen the link between atrophy rates and disease modificationInevitably disease modifying drug(s) are required to strengthen the link between atrophy rates and disease modification