Dissociation between cutaneous silent period and laser evoked potentials in assessing neuropathic pain

Chronic neuropathic pain is more than a perception: Systems and methods for an integral characterization

The management of chronic neuropathic pain remains a challenge, because pain is subjective, and measuring it objectively is usually out of question. However, neuropathic pain is also a signal provided by maladaptive neuronal activity. Thus, the integral management of chronic neuropathic pain should not only rely on the subjective perception of the patient, but also on objective data that measures the evolution of neuronal activity. We will discuss different objective and subjective methods for the characterization of neuropathic pain. Additionally, the gaps and proposals for an integral management of chronic neuropathic pain will also be discussed. The current management that relies mostly on subjective measures has not been sufficient, therefore, this has hindered advances in pain management and clinical trials. If an integral characterization is achieved, clinical management and stratification for clinical trials could be based on both questionnaires and neuronal activity. Appropriate characterization may lead to an increased effectiveness for new therapies, and a better quality of life for neuropathic pain sufferers.

Neurophysiologic assessment of small fibre damage in chemotherapy-induced peripheral neuropathy

OBJECTIVE

In patients with chemotherapy-induced peripheral neuropathy (CIPN), demonstration of small fibre (SF) damage is important to understand chronic late effects.

METHODS

Thirty patients having complaints compatible with possible CIPN following treatment with oxaliplatin or docetaxel were compared with 27 healthy subjects. All subjects were evaluated with quantitative sensory testing (QST) assessing SF function and laser evoked potentials (LEP). In addition, SF-damage was assessed using cutaneous silent periods evoked with electrical (El-CSP) and laser (Ls-CSP) stimuli.

RESULTS

For LEP, N2P2 amplitudes were significantly smaller in patients than controls in both upper (P = 0.007) and lower extremities (P = 0.002), and the N1 amplitude in upper extremities of patients were significantly smaller than in controls (P = 0.001). SF-QST, LEP, Ls-CSP, and El-CSP were abnormal in 10 (33.3%), 16 (53.3%), 19 (63.3%), and 24 (80%) of CIPN patients, respectively.

CONCLUSIONS

In patients with possible CIPN, El-CSP and Ls-CSP were more often abnormal than LEP and QST. This is probably because El-CSP and Ls-CSP inform mainly about peripheral nociceptive fibres, while LEP and QST inform about peripheral and central nociceptive pathways together.

SIGNIFICANCE

LEP and QST are established methods to detect SF-damage. El- and Ls-CSP might help clinicians in diagnosing SF-damage.

Elevated pain threshold in patients with asymptomatic diabetic neuropathy: an intraepidermal electrical stimulation study

INTRODUCTION

The loss of epidermal nerve fibers is regarded as an early pathological change in human diabetes. We investigated epidermal Aδ nerve fiber function by examining pain threshold by means of intraepidermal electrical stimulation (IES) in early diabetic neuropathy.

METHODS

We recruited 20 asymptomatic diabetic patients. Eighteen age-matched, healthy subjects served as controls. We placed the IES electrode onto the skin of the foot dorsum and delivered weak electrical stimulation. We defined pain threshold as the minimum electrical intensity at which a subject felt a pricking sensation.

RESULTS

The mean pain thresholds in the patient group were significantly higher (0.053 ± 0.036 mA; P < 0.01) than in the control group (0.027 ± 0.006 mA).

CONCLUSION

We confirmed that the pain threshold was elevated in early diabetic neuropathy. We conclude that the IES electrode is a useful tool to evaluate early diabetic polyneuropathy. Muscle Nerve 54: 146-149, 2016.

Cutaneous silent period recordings in demyelinating and axonal polyneuropathies

OBJECTIVE

To investigate the cutaneous silent period (CSP), a spinal inhibitory reflex mainly mediated by A-delta fibres, in demyelinating and axonal polyneuropathy (PNP) and evaluate whether CSP parameters differ between patients with and without neuropathic pain.

METHODS

Eighty-four patients with demyelinating PNP, 178 patients with axonal PNP and 265 controls underwent clinical examination, DN4 questionnaire, standard nerve conduction study, motor-root stimulation and CSP recordings from abductor digiti minimi. We calculated the afferent conduction time of CSP (a-CSP time) with the formula: CSP latency-root motor evoked potential latency.

RESULTS

In the demyelinating PNP group the a-CSP time was significantly longer; in the axonal PNP group, CSP duration was shorter than the demyelinating group (p=0.010) and controls (p=0.001). CSP parameters were not different between patients with and without neuropathic pain.

CONCLUSIONS

The abnormality of a-CSP time in the demyelinating PNP group suggests the crucial role of A-delta fibres in the mechanism of CSP; the shorter CSP duration in the axonal PNP group supports the strong influence of the number of axons on this parameter. Our study suggests that neuropathic pain could be related to pathophysiological mechanisms differing from mere A-delta fibre loss.

SIGNIFICANCE

CSP evaluation is effective in detecting A-delta fibre dysfunction in axonal as well as demyelinating PNP.

Assessment of symptomatic diabetic patients with normal nerve conduction studies: utility of cutaneous silent periods and autonomic tests

Established electrophysiological methods have limited clinical utility in the diagnosis of small-fiber neuropathy (SFN). In this study, diabetic patients with clinically diagnosed SFN were evaluated with autonomic tests and cutaneous silent periods (CSPs). Thirty-one diabetic patients with clinically suspected SFN and normal nerve conduction studies were compared with 30 controls. In the upper extremities (UE), the CSP parameters did not differ statistically between the patient and control groups, whereas, in the lower extremities (LE), patients had prolonged CSP latencies (P = 0.018) and shortened CSP durations (P < 0.001). The sensitivity of the CSP duration was 32.6%, and the specificity was 96.7%. The expiration-to-inspiration ratios and amplitudes of the sympathetic skin responses in the lower extremities were also reduced. Our findings indicate that the diagnostic utility of CSPs was higher than that of the autonomic tests to support the clinically suspected diagnosis of SFN.

Where is the core of the volcano? The undetermined origin of primary restless legs syndrome

An association between small fiber neuropathy and primary Restless Legs Syndrome (RLS) is suggested since both of them share common characteristics. Our aim was to investigate the existence of autonomic neuropathy on the basis of autonomic tests. The patients and the age-matched controls were evaluated with Neuropathy Symptom Profile and Autonomic Symptom Profile, nerve conduction studies (NCS), and autonomic tests. Patients suffered from neuropathic and autonomic complaints obviously. There was no significant difference for NCS, heart rate variability tests, and sympathetic skin responses (SSRs) among patients and controls. Since both the NCSs and the autonomic tests were within normal, the complaints were considered to be the consequences of the problem in sensory integration due to the dysfunction of the caudal diencephalic A11 group, rather than a neuropathic process. The cardiac autonomic imbalance possibly emerges as a consequence of arousal periods prior to or during the Periodic Leg Movements (PLM) episodes during sleep, but not due to autonomic neuropathy.