Serum B12, Homocysteine Levels, and their Effect on Peripheral Neuropathy in Parkinson's Disease: Indian Cohort

Longitudinal evaluation of polyneuropathy in Parkinson's disease

BACKGROUND

Increasing evidence indicates a higher prevalence of polyneuropathy (PNP) in Parkinson's disease (PD). However, the involvement of large fiber neuropathy in PD still remains poorly understood. Given the lack of longitudinal data, we investigated the course of PNP associated with PD.

METHODS

In total, 41 PD patients underwent comprehensive clinical evaluation including motor and non-motor assessments as well as nerve conduction studies at baseline and at 2 years of follow-up. The definition of PNP was based on electrophysiological standard criteria. Common causes of PNP were excluded.

RESULTS

At baseline, PNP was diagnosed in 65.85% of PD patients via electroneurography. Patients with PNP presented with higher age (p = 0.019) and PD motor symptom severity (UPDRS III; p < 0.001). Over the course of 2 years, PNP deteriorated in 21.95% of cases, and 26.83% remained without PNP. Deterioration of nerve amplitude was most prevalent in the median sensory nerve affecting 57.58% of all PD cases with an overall reduction of median sensory nerve amplitude of 45.0%. With regard to PD phenotype, PNP progression was observed in 33.33% of the tremor dominant and 23.81% of the postural instability/gait difficulties subtype. Decrease of sural nerve amplitude correlated with lower quality of life (PDQ-39, p = 0.037) and worse cognitive status at baseline (MoCA, p = 0.042).

CONCLUSION

The study confirms the high PNP rate in PD, and demonstrates a significant electrophysiological progression also involving nerves of the upper extremities. Longitudinal studies with larger cohorts are urgently needed and should elucidate the link between PD and PNP with the underlying pathomechanisms.

Parkinson's disease and vitamins: a focus on vitamin B12

Parkinson's disease (PD) has been linked to a vast array of vitamins among which vitamin B12 (Vit B12) is the most relevant and often investigated specially in the context of intrajejunal levodopa infusion therapy. Vit B12 deficiency, itself, has been reported to cause acute parkinsonism. Nevertheless, concrete mechanisms through which B12 deficiency interacts with PD in terms of pathophysiology, clinical manifestation and progression remains unclear. Recent studies have suggested that Vit B12 deficiency along with the induced hyperhomocysteinemia are correlated with specific PD phenotypes characterized with early postural instability and falls and more rapid motor progression, cognitive impairment, visual hallucinations and autonomic dysfunction. Specific clinical features such as polyneuropathy have also been linked to Vit B12 deficiency specifically in context of intrajejunal levodopa therapy. In this review, we explore the link between Vit B12 and PD in terms of physiopathology regarding dysfunctional neural pathways, neuropathological processes as well as reviewing the major clinical traits of Vit B12 deficiency in PD and Levodopa-mediated neuropathy. Finally, we provide an overview of the therapeutic effect of Vit B12 supplementation in PD and posit a practical guideline for Vit B12 testing and supplementation.

Prevalence and Risk Factors of Peripheral Neuropathy in Parkinson's Disease

Introduction

A lesser studied aspect of Parkinson's disease (PD) is its associated peripheral sensory-motor neuropathy. Peripheral neuropathy is an intriguing aspect of PD, a problem not given sufficient attention and which if tackled properly could make a difference to the multifaceted sufferings of the PD patient. Studies regarding the prevalence of peripheral neuropathy and its risk factors in patients with PD are scarce from the Indian subcontinent.

Methods

This prospective observational study was conducted in a tertiary care teaching hospital in South India. Patients diagnosed with idiopathic Parkinson's disease (IPD) were screened and enrolled. All the patients underwent detailed evaluation of symptoms, signs, and electrophysiology (Nerve conduction study, Sympathetic skin response), stimulated skin wrinkling with Eutectic Mixture of Local Anesthetics. Patients found to have large/small fiber neuropathy underwent additional tests to exclude other causes of neuropathy.

Results

A total of 154 patients with IPD were enrolled in the study (mean age: 61.96 ± 9.15 years, mean duration of disease was 4.08 ± 3.16 years). The mean Hoehn and Yahr (H and Y) score was 2.3 ± 0.825 and the mean Unified Parkinsons Disease Rating Scale (UPDRS)-3 score in the ON state was 23.07 ± 11.14. The mean cumulative levodopa dose was 482.68 ± 651.76 (median: 292; range: 4728.57) grams. Peripheral neuropathy was found in 49 patients (31.8%), large fiber in 28 (18.2%) and small fiber in 47 (30.5%); an overlap of large and small fiber neuropathy was seen in 26 patients (16.9%). Around 34% of patients had serum homocysteine levels >20 mg/dl. In univariate analysis, duration of disease, levodopa cumulative dose, serum homocysteine level, H and Y score, UPDRS-3 ON score, Toronto Clinical Neuropathy Score (P < 0.001 for all), age at presentation, and rigidity predominant presentation (P = 0.02 for both) were associated with large fiber neuropathy. All of these variables were also associated with the presence of small fiber neuropathy (P = 0.004 for age at presentation and P < 0.001 for rest), except the type of PD presentation. However, in multivariate logistic regression analysis, only duration of disease, levodopa cumulative dose, and H and Y score were associated with the presence of large and small fiber neuropathy.

Conclusions

In our cohort, majority of the patients were in early-stage PD and around one-fifth and one-third of patients suffer from large and small fiber polyneuropathy, respectively. Large and small fiber neuropathy in PD is mainly associated with duration of disease, levodopa cumulative dose, and H and Y score.

Changes of Peripheral Nerve Function and Vitamin B12 Level in People With Parkinson's Disease

Background and Purpose: Peripheral nerve function plays an important role in balance control. Impairment of peripheral sensory information appears in people with Parkinson's disease (PD). Furthermore, there is a link between peripheral nerve disorders and vitamin B₁₂ level. Here, we studied whether there were deficits of peripheral nerve function and vitamin B₁₂ level, which may lead to decreased postural stability in PD.

Methods: Fifty PD and 50 age-matched healthy subjects were enrolled in the study. This study evaluated folic acid and vitamin B₁₂ levels in serum. Postural balance was studied according to the clinical Tinetti scale. Some comprehensive physiological assessments of peripheral nerve functions, including peripheral sensation, the perception of temperature, pain, and touch sensations, were also undertaken in this study.

Results: Compared with the control group, vitamin B₁₂ and folic acid were decreased in PD (P < 0.05). Furthermore, the PD group exhibited declines in peripheral nerve functions, including touch, temperature, pain, and nerve conduction velocity (P < 0.05). Statistical tests identified a significant association between decreased peripheral nerve function and poor balance according to the Tinetti scale (P < 0.05). Low vitamin B₁₂ levels were also associated with deficits of peripheral nerve function, cumulative levodopa dose, and poor balance in PD (P < 0.05).

Conclusions: Data suggested that peripheral nerve function was impaired in people with PD. Deficits of sensory input and low vitamin B₁₂ level may contribute to balance deficits in PD.