A latent class analysis of psychological disturbance in Parkinson's disease

Psychological symptoms are common in Parkinson's disease (PD). Psychological symptoms do not respond to psychotropic medications as well in patients with PD as in patients with psychiatric illnesses who do not have PD. Evidence that PD patients can be classified into distinct psychological symptom subgroups is conflicting. This study sought to examine potential psychological heterogeneity in PD with a broader range of instruments than has been used in previous studies.

A comprehensive battery of psychological measures assessing dysphoria, apathy, anhedonia, anxiety, and negative affect was administered to 95 PD patients without global cognitive impairment. Latent class analysis was used to identify subgroups of patients based on continuous variables derived from the psychological battery. Multinomial regression was used to examine predictors of classification.

The latent class analysis identified three subgroups with incremental levels of psychopathology across most symptom domains. One exception was a greater level of affective flattening in the "psychologically healthy" group compared with the "moderate symptoms" group. Greater motor dysfunction and less education were associated with greater severity of psychological symptoms.

These results support high psychological co-morbidity in PD, which complicates the treatment of individual symptoms. In addition, emotional blunting and anhedonia may be less indicative of widespread psychological distress than anxiety, dysphoria, and cognitive aspects of apathy. Clinicians should be aware that PD patients with greater motor dysfunction and less education are at greater risk not only for depression but also for a variety of other psychological symptoms that may not be routinely assessed.