Disturbed sensory perception of changes in thermoalgesic stimuli in patients with small fiber neuropathies

Adaptation to tonic heat in healthy subjects and patients with sensory polyneuropathy

Adaptation to a constant sensory stimulus involves many sites along the path of sensory volleys towards perception. The evaluation of such phenomenon may be of clinical interest. We studied adaptation to a constant temperature stimulus in healthy subjects to set normative data, and in patients with sensory polyneuropathy (SPN), as proof of concept. Twenty-six healthy subjects and 26 patients with SPN in the context of chemotherapy treatment with oxaliplatin for colon cancer were instructed to express through an electronic VAS system (eVAS) the level of sensation felt when a thermode set at either 39º, 41º, 43º, 45º or 47º was applied to their ventral forearm. The eVAS recordings showed typically an abrupt onset that slowed to approach maximum sensation and continued with a slow decrease indicating adaptation. The time to respond (TR), the velocity of the initial response (VR), the maximum sensation (MA), the time to reach MA (MAt), the onset of adaptation (AO), and the decrease in the sensation level with respect to MA at 30 s after stimulus application (SL30), were dependent on the temperature level in all subjects. However, patients showed significantly delayed TR, slowed VR, decreased MA, delayed AO, and reduced SL30, with respect to healthy subjects. Differences were more pronounced at low temperature levels, with absent AO in 25 patients vs. 2 healthy subjects at temperatures of 39º and 41ºC. The study of adaptation to a constant temperature stimulus can furnish valuable data for the assessment of SPN patients.

Electrodiagnostic Testing of Small Fiber Neuropathies: A Review of Existing Guidelines

This article reviews the literature on neurophysiological techniques for the diagnosis of small fiber neuropathy. The review is focused on clinical approach to suspected small fiber neuropathy, letting aside techniques whose clinical applicability is doubtful. We include, however, the special techniques required to examine C and Aδ fibers, which cannot be evaluated directly with conventional neurophysiological methods. The most relevant publications are summarized and recommendations for the clinical assessment of small fiber neuropathy are provided.

Evolving concepts on the role of dyslipidemia, bioenergetics, and inflammation in the pathogenesis and treatment of diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is one of the most widespread and disabling neurological conditions, accounting for half of all neuropathy cases worldwide. Despite its high prevalence, no approved disease modifying therapies exist. There is now a growing body of evidence that DPN secondary to type 1 diabetes mellitus (T1DM) and type 2 diabetes mellitus (T2DM) represents different disease processes, with T2DM DPN best understood within the context of metabolic syndrome rather than hyperglycemia. In this review, we highlight currently understood mechanisms of DPN, along with their corresponding potential therapeutic targets. We frame this discussion within a practical overview of how the field evolved from initial human observations to murine pathomechanistic and therapeutic models into ongoing and human clinical trials, with particular emphasis on T2DM DPN and metabolic syndrome.

Evidence of neurophysiological improvement of early manifestations of small-fiber dysfunction after liver transplantation in a patient with familial amyloid neuropathy

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Detecting signs of neuropathy helps therapeutic decisions in familial amyloidosis.

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Psychophysical thermal testing may be the only test showing damage in small fibers.

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Quantitative signs of improvement may remain a few years after liver transplantation.

Introduction

Small fiber polyneuropathy (SFP) is a common heralding clinical manifestation of damage to the nervous system in patients with familial amyloidosis. The diagnosis of SFP is a significant factor in the decision to treat a previously asymptomatic gene carrier, as treatment would prevent irreversible nerve damage. This requires detection of the earliest but unequivocal signs of peripheral nerve involvement.

Case report

We present the case of a young female who was diagnosed of SFP, supported by data from quantitative sensory testing. She had preserved sensory nerve action potentials in the distalmost nerves of her feet and recordable nociceptive evoked potentials. She was successfully transplanted the liver from a previously healthy donor, and recovered fully of her symptoms and signs. Improvement was documented with repeated psychophysical and electrodiagnostic testing in the course of 4 years after transplantation.

Significance

This case illustrates the utility of psychophysical testing to support the diagnosis of SFP.

Pinprick Testing in Small Fiber Neuropathy: Accuracy and Pitfalls

OBJECTIVES

To assess the sensitivity, specificity, and predictive value of pinprick perception and its concordance with established laboratory measures in small fiber neuropathy.

METHODS

Fifty-six patients suspected of SFN underwent detailed evaluation and standardized quantitative sensory and autonomic testing. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value of pinprick sensation were determined.

RESULTS

Pinprick perception had relatively consistent results between modalities with moderate sensitivity (70%); combining the testing modalities increased the diagnostic yield. PPV of pinprick approached 89%; however, negative predictive value was 19%.

CONCLUSIONS

As a screening tool, pinprick has high PPV for SFN, but many patients are likely to be missed if they report unimpaired subjective perception of pinprick sensation. Multimodal testing is recommended in clinically suspected cases to positively rule out SFN.