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PART 1—GENERAL APPROACH TO RAPIDLY PROGRESSIVE DEMENTIAS
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CASE 32-1
A 64-year-old man presented with rapidly progressive, subacute, nonfluctuating dementia, and recurrent unprovoked falls. He had been well 8 months previously. At that point, the family noted the onset of apathy and problems with sleep. Two months later, the patient was noted to have problems with balance and gait, and had a number of unprovoked falls with gait unsteadiness and “dizziness.” He then developed jerky movements, especially in the arms. In the ensuing months, he had worsening disorientation and cognitive decline. He started having difficulties with recognizing relatives. He became withdrawn, akinetic, and mute. He was conscious, but did not have any meaningful reactions to voice commands.
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RAPIDLY PROGRESSIVE DEMENTIA AS A DIAGNOSTIC CATEGORY
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Why is this presentation consistent with a rapidly progressive dementia?
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Rapidly progressive progressive dementia (RPD) is a clinical diagnosis that has the following characteristics:
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Rapidly progressive dementia (RPD) refers to a dementing process that develops over a period of less than 2 years.1
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RPDs are a category of disease processes characterized by being diagnostic conundrums at presentation.
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There are certain characteristics that are common but not universal in RPDs:
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Rapid progression of cognitive decline
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Presence of movement disorders, in particular ataxia, gait disorders, or myoclonus
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Concomitant behavioral or psychiatric symptoms
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Epileptiform or periodic waveforms on EEG
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In the aforementioned vignette, the time course, the presence of ataxia, gait problems, myoclonus, and akinetic mutism point the clinician toward a diagnosis of RPD.
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Why is it important to recognize RPD and differentiate it from more common chronic dementias?
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Many conditions presenting as RPD are associated with high levels of morbidity and mortality. Early recognition allows prognostication and gives the family time to plan for eventualities.
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Some of these conditions are treatable if detected early.
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The general approach to evaluating these patients is different in RPDs and chronic dementias.
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Epidemiologically, what are the most common causes of RPD?
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A study conducted at the University of California San Francisco (UCSF) evaluated 178 patients with RPD and found 62% to be due to prion diseases. Of the remaining cases, 39% were neurodegenerative, 22% were autoimmune, 6% were infectious, another 6% were psychiatric, 14% were due to other causes, and 12% did not have a definitive diagnosis. It is likely that these data reflect a referral bias to UCSF given its reputation in the field of prion disease.2
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In other tertiary settings, prion diseases may contribute less to the overall case mix. For example, a study of 68 consecutive patients referred for RPD to an Athens clinic consisted of 21 patients with neurodegenerative dementias (AD followed by frontotemporal dementias and Lewy body disease), 9 with vascular dementia, another 9 with Creutzfeldt-Jakob disease (CJD), 4 people with normal-pressure hydrocephalus (NPH) (Figure ...