Somatoform Symptoms in Parkinson Disease.

Background: Co-occurring somatoform symptoms complicate the diagnosis and treatment of Parkinson disease (PD).

Objective: To learn more about the relationship between somatoform symptoms and PD by comparing demographic and clinical features across PD groups differing in somatoform symptom severity.

Method: Using standardized Brief Symptom Inventory-18 (BSI-18) scores to measure somatoform symptom severity, we assigned 1093 individuals with PD to one of four subgroups using comparisons to normative means: low (M < -½ SD), average (M ± ½ SD), high (M +½ SD to +1 SD), very high (M > +1 SD). We used demographics and disease severity measures to assess each subgroup.

Results: Most of the individuals with PD (56%) had high or very high somatoform symptom levels. Increased somatoform symptom levels were associated with female gender, lower socioeconomic status, greater disease duration, increased PD severity (Total Unified Parkinson's Disease Rating Scale), greater disability (Older Americans Resource and Services Disability subscale), increased BSI-18 Depression and Anxiety subscale scores, lower cognitive function (Mini-Mental State Examination), lower self-efficacy scores (Self-Efficacy to Manage Chronic Disease Scale), lower quality of life scores (SF-12 Health Status Survey), and greater medical comorbidity (Cumulative Illness Rating Scale-Geriatrics) (all comparisons: P < 0.001). We found no significant between-group differences for age, race, or marital status.

Conclusion: Somatoform symptom severity in individuals with PD is associated with greater PD severity and disability and is more common in females and in individuals with low socioeconomic status. Greater awareness of somatoform symptoms should help improve PD treatment.