There are numerous other causes of an extrapyramidal syndrome manifesting as parkinsonism apart from Parkinson's disease (see previous chapter). Traditionally, these are listed etiologically as shown in Table 34.1. In this list three broad groups emerge namely that referred to as the parkinsonism-plus syndromes (also called atypical parkinsonian syndromes), the symptomatic or secondary parkinsonian conditions and the hereditary/heredodegenerative disorders (Table 34.1). The parkinsonism-plus syndromes are so called because they are multisystem degenerations and have other features in addition to parkinsonism. This older classification, although useful, has its limitations because the divisions drawn are somewhat artificial and there is a fair amount of overlap in the disorders listed under the different subheadings. For example, additional clinical features can also be present in disorders in the two groups apart from the parkinson-plus disorders and it is being realized that a genetic basis may even underlie parkinsonian disorders thought to be sporadic like progressive supranuclear palsy (PSP). Great advances at the molecular, ultrastructural and genetic level are leading to a newer way of classifying many of these degenerative diseases affecting the basal ganglia causing extrapyramidal syndromes (Dickson, 1997; Spillantini, 1999). Many parkinsonian syndromes can now be viewed as being caused by the genetic or sporadic occurrence of diseases characterized on the basis of cytoskeletal pathology and staining of particular proteins, for example, alphasynucleinopathies where alpha-synuclein is present (Spillantini, 1999; Goedert, 2001) or taupathies wherein there is deposition of tau protein (Morris et al., 1999a). This way, many of the disorders listed in Table 34.1 can now be reclassified as shown in Tables 34.2 and 34.3 on a molecular basis. Thus PSP and corticobasal degeneration and the inherited condition of frontotemporal dementia parkinsonism as well as dementia pugilistica or encephalitislethargica from the secondary parkinsonism division are all grouped together as ‘taupathies’, while multiple system atrophy (MSA) and Parkinson's disease and dementia with Lewy bodies go together as ‘alpha-synucleinopathies’ (Spillantini et al., 1998a).

It is beyond the scope of this chapter to detail each of the conditions causing parkinsonism listed in Table 34.1, hence this chapter will focus on some of the conditions most likely to be confused with Parkinson's disease, namely progressive supranuclear palsy (PSP), corticobasal degeneration (CBD) and multiple system atrophy (MSA) among the parkinsonism-plus syndromes with a brief mention of other related conditions as well as some secondary or symptomatic parkinsonian disorders.