Somatosensory symptoms in unmedicated de novo patients with idiopathic Parkinson’s disease

Sensory Neuropathy in Parkinson Disease: Electrodiagnostic Evaluation

The relationship between Parkinson Disease (PD) and peripheral neuropathy (PN) has gained attention in recent years. There is increasing evidence of a-synuclein deposition and pointing to a form of small fiber neuropathy intrinsic to PD, medium-large fiber PN is also a relatively frequent and potentially severe complication in advanced levodopa-treated PD, but degenerative factors and vitamin deficiency were related. Objective: To determine the neurophysiological characteristics of patients with PD and the clinical manifestations of suspected PN. Methods: We performed a cross-sectional study between January 2014 and December 2017, of 36 patients diagnosed with PD who were referred for electrodiagnostic studies (EDX) with suspected clinical PN. We performed electromyography of five muscle or more (brachial biceps, first dorsal interosseous, thumb abductor, anterior tibial, medial gastrocnemius and short finger extensor), and nerve conduction/velocity studies on fibular and tibial nerves (motor) sural and superficial fibular nerves (sensory) and median and ulnar, (both motor and sensory). Results: Twenty-one females (58.3%) with an average age of 69.6 years and fifteen males (41.7%) with an average age of 68.0 years who were submitted for EDX were included in this study. All had a tremor and the average evolution of PD was 5 years. Thirty-two patients were receiving oral levodopa treatment. EDX of twenty-two patients demonstrated neuropathy abnormalities, and in 90.9% of these patients, sensory neuropathy was confirmed. The most common nerve found to be compromised was the superficial fibular nerve (55.0%), followed by the sural (50.0%). Conclusions: Sensory neuropathy was the main finding. Diagnosing PN based on symptom prevalence assessed by checklists and questionnaire has a risk of overestimating the prevalence of PN. The age and the time of disease evolution were factors related to neuropathy. In our study we found that 39% of the patients did not have neuropathic alterations despite clinical suspicion, which opens up new questions about the mechanisms of PD neuropathy and the possibility of fine fiber neuropathy in these patients, motivating further research.

Quantitative Sensory Testing (QST) in Drug-Naïve Patients with Parkinson's Disease

BACKGROUND

Pain is highly prevalent in patients with Parkinson's disease (PD), but underlying pathophysiological mechanisms are largely unclear. Alterations in somatosensory processing might contribute to sensory abnormalities in PD.

OBJECTIVE

This study investigated sensory processing in PD patients.

METHODS

We used the standardized "Quantitative Sensory Testing" (QST) protocol (German Research Network on Neuropathic Pain) to investigate 13 somatosensory parameters in 19 PD patients naïve to dopaminergic medication and 19 healthy controls matched for age, gender, and handedness. We tested for differences in sensory parameters between i) drug-naïve PD patients and healthy controls, ii) patients' more and less affected body side, and iii) for an association of somatosensory parameters with disease-specific factors.

RESULTS

We did not observe any significant group differences in somatosensory parameters between PD patients and healthy subjects. In PD patients, QST mean z-scores did not differ between the predominantly and the less affected body side, PD patients with and without PD-specific chronic pain or between different PD subtypes. Age, but not PD disease severity, was associated with a greater loss of function in thermal and mechanical detection thresholds.

CONCLUSIONS

Somatosensory processing, as assessed with the well-established QST protocol, was normal in drug-naïve PD patients. Thus, somatosensory abnormalities previously reported in medicated PD patients might rather be a result of dopaminergic medication, or may occur later in the course of the disease or with increasing age.

Loss of cutaneous large and small fibers in naive and l-dopa-treated PD patients

OBJECTIVE

To study small and large fiber pathology in drug-naive and l-dopa-treated patients affected by Parkinson disease (PD) in early phases, before the occurrence of neuropathic electrophysiologic abnormalities.

METHODS

We enrolled 85 patients with idiopathic PD (male/female 49/36, age 61.3 ± 9.7 years) without electrophysiologic signs of neuropathy, including 48 participants naive to l-dopa treatment. All patients underwent clinical, functional, and morphologic assessment of sensory and autonomic nerves through dedicated questionnaires, quantitative sensory testing, sympathetic skin response, dynamic sweat test, and punch biopsies from glabrous and hairy skin. Sensory and autonomic innervation was visualized with specific antibodies and analyzed by confocal microscopy. Data were compared with those obtained from sex- and age-comparable healthy controls. In 35 patients, skin biopsies were performed bilaterally to evaluate side-to-side differences.

RESULTS

Intraepidermal nerve fiber density was lower in patients compared to controls in all the examined sites (p < 0.001). The loss was higher in the more affected side (p < 0.01). A loss of autonomic nerves to vessels, sweat glands, and arrector pili muscles and of Meissner corpuscles and their myelinated endings in glabrous skin was found (p < 0.001). Patients showed increased tactile and thermal thresholds, impairment of mechanical pain perception, and reduced sweat output (p < 0.001). The naive and l-dopa-treated groups differed only for Meissner corpuscle density (p < 0.001).

CONCLUSIONS

Both large and small fiber pathology occurs in the early stages of PD and may account for the sensory and autonomic impairment. l-Dopa affects the 2 populations of fibers differently.