Diagnostic criteria for PD-D
Historically, diagnosis of PD-D in clinical practice was made empirically, while diagnosis in research studies was mainly based on the Diagnostic and Statistical Manual (DSM)-IV criteria, which group ‘dementia due to PD’ along with ‘other causes of dementia’ without providing specifics. This gap was recognized by the Movement Disorder Society (MDS), and a Task Force of international experts was called together to develop specific clinical diagnostic criteria for PD-D .
According to these criteria, the first step in the diagnostic process is the diagnosis of PD in accordance with the Queen Square (UK) Brain Bank criteria for the diagnosis of PD. The second step involves identification of a dementia syndrome diagnosed on the basis of history and clinical and mental examination, with insidious onset, slow progression, and typical clinical features (Table 20.4). The later steps involve screening for other conditions, in the presence of which diagnosis of dementia would be uncertain or impossible. Diagnostic certainty relies on the presence of typical or atypical cognitive and behavioural features as well as the presence or absence of other conditions. Based on these features, diagnostic criteria are described for ‘probable’ and ‘possible’ PD-D (Table 20.5). Probable PD-D is diagnosed when dementia with typical features develops on the background of established PD, in the absence of any other conditions which may contribute to, or cause, dementia. A diagnosis of possible PD-D is justified when either there is one or more atypical clinical feature, or in the presence of one or more conditions which would make the diagnosis of PD-D uncertain. In a validation study including 299 PD patients, agreement between MDS Task Force and DSM-IV criteria was substantial; MDS Task Force criteria were, however, more sensitive than DSM-IV for the diagnosis of PD-D. Old age, absence of psychiatric symptoms, and severe motor impairment were the likely factors hindering the diagnosis of PD-D .