Atypical PKAN. The clinical features of atypical PKAN are more varied than those of early-onset disease. Onset is in the first three decades (mean age: 13.6 years). Progression of the atypical form is slower than the classic form, and presenting features are distinct, usually involving speech as either the sole presenting feature or part of the constellation of problems. The speech defects include palilalia (repetition of words or phrases), tachylalia/tachylogia (rapid speech of words and/or phrases), and dysarthria (poor articulation, slurring) [Benke et al 2000, Benke & Butterworth 2001].
Psychiatric symptoms including personality changes with impulsivity and violent outbursts, depression, and emotional lability are common in late-onset disease. Affected individuals may also exhibit motor and verbal tics, obsessive-compulsive behavior, and, rarely, psychotic symptoms [Pellecchia et al 2005, del Valle-López et al 2011].
As with early-onset disease, cognitive impairment may be part of the late-onset PKAN phenotype, but additional investigations are needed. Freeman et al [2007] found that later age of onset is correlated with less intellectual and adaptive behavior impairment.
Motor involvement is usually a later feature, although individuals with motor involvement often have been described as clumsy in childhood and adolescence. Spasticity, hyperreflexia, and other signs of corticospinal tract involvement are common and eventually limit ambulation. Conspicuously reminiscent of Parkinson disease, “freezing” during ambulation (especially when turning corners or encountering surface variations) is observed [Guimaraes & Santos 1999].
An essential tremor-like syndrome has also been reported [Yamashita et al 2004].
Retinopathy is rare in atypical disease, and optic atrophy has not been associated with atypical disease.