Objective: To study the incidence of insulin resistance (IR) in people with Parkinson’s Disease (PD) and its relationship with motor and non-motor symptoms of the disease.

Background: IR and diabetes have been associated with the development of PD and there is evidence that IR might contribute to motor and cognitive deterioration. IR is a potentially reversible state and may provide a target for drugs and lifestyle interventions promoting neuro-protection. However, the incidence of IR in PD is poorly studied.

Methods: 123 non-diabetic idiopathic PD people (91 M, 32 F, average age of 66.8±10.4) attending the movement disorders clinic at Cedars Sinai Medical Center in Los Angeles were tested for fasting insulin, glucose and hemoglobin A1c (HbA1c). HOMA index was calculated by the formula: (Insulin x Glucose) / 405 = HOMA index. A cutoff HOMA of 2.0 was used to identify IR. Body Mass Index (BMI) and levodopa equivalents (LED) were also collected. Additional testing of motor and non-motor features was performed, including UPDRS, MoCA, NMSQ and PDQ-39. 

Results: 59 subjects (48%) had an abnormal HOMA index (range: 2.01 to 10.60), consistent with IR. An additional 12 subjects had abnormal HbA1c, for a total of 71 subjects (58%) with abnormal glucose metabolism. 86 subjects (75.6%) were overweight (BMI > 25) and 52 (60%) had IR. Also 8 of 37 (22%) people with normal BMI had IR. All but 1 (99.2%) non-diabetic PD patient with IR had normal fasting glucose levels, and 67/80 (84%) had normal HbA1c. HoMA abnormalities correlated with BMI (r=0.42, p<0.01) but not with HbA1c levels and LED. There was no correlation between HoMA index and UPDRS, NMSQ, MoCA and PDQ39 scores. 10/16 subjects with abnormal MoCA scores had IR, with a mean HoMA of 2.24 

Conclusions: Nearly half of non-diabetic people with PD in our study population had a HoMA index consistent with IR, which correlated with increasing BMI. The majority of individuals with IR had normal fasting glucose and HbA1c levels. Therefore, IR would go undetected by usual diabetic screening techniques. We conclude that IR may be an undiagnosed problem in a large proportion of people with PD, in particular if overweight. While we could not find specific correlation of IR with motor and non-motor PD symptoms, this data will deserve further attention and research given the putative role of IR in accelerating the progression of non-motor and motor features of PD. 

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MDS Abstracts - https://www.mdsabstracts.org/abstract/insulin-resistance-in-non-diabetic-people-with-parkinsons-disease/