Patients with PD–T2DM had higher Movement Disorders Society Unified Parkinson’s Disease Rating Scale (MDS-UPDRS) III scores; total MDS-UPDRS scores; Parkinson’s Disease Questionnaire-39 (PDQ-39) scores; and interleukin (IL)-6, IL-1β, tumour necrosis factor alpha (TNF-α) and IL-4 levels than patients with PD (p < 0.05). Here, IL4 is linked to type 2 diabetes mellitus.