Neuropathies of the foot

A combined functional dorsal nerve model of the foot

The nerves in the skin surface of the foot are comprised of unmyelinated smaller somatic nerves and larger myelinated sensory nerves. Current diagnostic methods are unable to evaluate combined nerve conduction velocity (NCV) from both unmyelinated smaller somatic nerve (USSN) and myelinated larger nerves (MLN) respectively. Computational models may provide an alternative tool to determine the NCV of the combined nerve. Therefore, a combined functional dorsal nerve model (CFDNM) of the various dorsal nerves along with its associated nerve ending of the human foot is proposed and constructed. The combined dorsal nerve model consists of synthetic USSN (SUSSN) and dorsal MLN of the foot. The unmyelinated as well as myelinated electrophysiological nerve models were used to simulate selected SUSSN and MLN of the foot by injecting an external stimulus at the most distal part of SUSSN of the foot through the use of bidomain model. Results from our work demonstrated that the action potential propagated from the most distal part to proximal part of distinct dorsal nerves of the foot, e.g., the simulated NCV of the combined intermediate dorsal cutaneous nerve (IDCN) of the foot was 28.4 m s^-1. The CFDNM will provide a vital tool for diagnosis initially small fibre neuropathy (SFN) by computing NCV in the prospective studies.

An Update on Posterior Tarsal Tunnel Syndrome

Posterior tarsal tunnel syndrome (PTTS) is an entrapment neuropathy due to compression of the tibial nerve or one of its terminal branches within the tarsal tunnel in the medial ankle. The tarsal tunnel is formed by the flexor retinaculum, while the floor is composed of the distal tibia, talus, and calcaneal bones. The tarsal tunnel contains a number of significant structures, including the tendons of 3 muscles as well as the posterior tibial artery, vein, and nerve. Focal compressive neuropathy of PTTS can originate from anything that physically restricts the volume of the tarsal tunnel. The variety of etiologies includes distinct movements of the foot, trauma, vascular disorders, soft tissue inflammation, diabetes mellitus, compression lesions, bony lesions, masses, lower extremity edema, and postoperative injury. Generally, compression of the posterior tibial nerve results in clinical findings consisting of numbness, burning, and painful paresthesia in the heel, medial ankle, and plantar surface of the foot. Diagnosis of PTTS can be made with the presence of a positive Tinel sign in combination with the physical symptoms of pain and numbness along the plantar and medial surfaces of the foot. Initially, patients are treated conservatively unless there are signs of muscle atrophy or motor nerve involvement. Conservative treatment includes activity modification, heat, cryotherapy, non-steroidal anti-inflammatory drugs, corticosteroid injections, opioids, GABA analog medications, tricyclic antidepressants, vitamin B-complex supplements, physical therapy, and custom orthotics. If PTTS is recalcitrant to conservative treatment, standard open surgical decompression of the flexor retinaculum is indicated. In recent years, a number of alternative minimally invasive treatment options have been investigated, but these studies have small sample sizes or were conducted on cadaveric models.

Constitutional risk factors for focal neuropathies in patients referred for electromyography

BACKGROUND AND PURPOSE

It is well established that patient-related constitutional features predispose to focal peripheral neuropathies. Some of these risk factors were investigated in common focal neuropathies encountered in patients referred for electromyography.

METHODS

Gender, age, height and body mass index (BMI) were analysed retrospectively as risk factors for 11 focal neuropathies. In all, 9686 patients (age range 18-96 years; 58% women) were included from three different centres, with identical methods and equipment.

RESULTS

High BMI was related to carpal tunnel syndrome (CTS), ulnar neuropathy at the elbow (UNE), combined CTS and UNE, meralgia paraesthetica and lumbar radiculopathy. In women, CTS and Morton's metatarsalgia were more common, whilst long thoracic neuropathies, suprascapular neuropathies and UNE were more common in men. Older age increased the risk for CTS, UNE, Morton's metatarsalgia and radiculopathies.

CONCLUSIONS

Age, gender and BMI are important risk factors for many common focal neuropathies.

Sclerosing alcohol injections for the management of intermetatarsal neuromas: A systematic review

An intermetatarsal neuroma is a plantar digital neuritis causing metatarsalgia of the affected inter-metatarsal space. At present the evidence to support the management of the condition is poor with only some quality evidence supporting the short-term management of intermetatarsal neuromas using steroid injections. Some authors have supported the use of alcohol sclerosing intra-lesional injections to treat intermetatarsal neuromas. Following a search of the evidence 11 articles were identified. The systematic review found that alcohol injections appear to be safe although some papers report a short-term side effect of a flogistic reaction and there are variances in the alcohol concentration used and guiding verses not guiding the injection using ultrasound imaging. Some of the evidence may suggest a sclerosing histological effect of the nerve. However, all the studies reviewed present a research design offering a low level of evidence that is open to methodological biases and interpretation. Thus, this review found insufficient high-quality research evidence to afford conclusions on the management of intermetatarsal neuromas with alcohol sclerosing agent injections.

The Tinel sign has no diagnostic value for nerve entrapment or neuropathy in the legs

INTRODUCTION

The presence of a Tinel sign in leg nerves has been proposed as a criterion for decompressive surgery in polyneuropathy. We investigated the diagnostic yield of the Tinel sign for nerve entrapment and for distal symmetrical peripheral neuropathy (DSPN).

METHODS

We prospectively tested for the Tinel sign at 3 sites of possible nerve entrapment per leg in 91 patients. Entrapment was defined using nerve conduction data. We also investigated whether the number of sites at which the Tinel sign was present identified patients with DSPN.

RESULTS

Sensitivity of the Tinel sign for nerve entrapment was low (29%, 44%, and 17%) for the 3 sites, and specificity was moderate (86%, 75%, and 81%). In the subgroup with DSPN, sensitivity was extremely low (0%, 20%, and 8%), and specificity was moderate (91%, 79%, and 73%). The number of sites with a Tinel sign did not identify patients with DSPN.

CONCLUSION

The Tinel sign does not reliably indicate nerve entrapment or DSPN. Muscle Nerve 54: 25-30, 2016.

Anterior tarsal tunnel syndrome: a misunderstood and a misleading entrapment neuropathy

Anterior tarsal tunnel syndrome (ATTS) is a rare entrapment neuropathy of the deep peroneal nerve beneath the extensor retinaculum on the top of the ankle. ATTS is often asymptomatic or olygosymptomatic. There are few reports describing the ATTS. We describe the clinical and electrophysiological features of 85 patients with unilateral or bilateral ATTS prospectively collected between January 2000 and December 2010 in our laboratory of Clinical Neurophysiology. This entrapment neuropathy remains poorly diagnosed and it might be misleading when performing a diagnostic EMG-ENG examination for suspected polyneuropathy or lumbosacral radiculopathy.

Compression and entrapment neuropathies

Peripheral nerve entrapments are frequent. They usually appear in anatomical tunnels such as the carpal tunnel. Nerve compressions may be due to external pressure such as the fibular nerve at the fibular head. Malignant or benign tumors may also damage the nerve. For each nerve from the upper and lower limbs, detailed clinical, electrophysiological, imaging, and therapeutic aspects are described. In the upper limbs, carpal tunnel syndrome and ulnar neuropathy at the elbow are the most frequent manifestations; the radial nerve is less frequently involved. Other nerves may occasionally be damaged and these are described also. In the lower limbs, the fibular nerve is most frequently involved, usually at the fibular head by external compression. Other nerves may also be involved and are therefore described. The clinical and electrophysiological examination are very important for the diagnosis, but imaging is also of great use. Treatments available for each nerve disease are discussed.

Focal conduction block in a case of tarsal tunnel syndrome

We report a case of tarsal tunnel syndrome (TTS) with focal conduction block across the tarsal tunnel (TT). A 46-year-old woman had pain in the left foot, sensory loss on the plantar surface, and positive Tinel sign over the TT. TTS was confirmed by magnetic resonance imaging (MRI) scan and surgery. Motor nerve conduction studies showed focal conduction block across the TT. Conduction block has rarely been reported in TTS. In this case, conduction block provides evidence for focal demyelination as the primary pathological process in TTS.

Ten-year follow-up of peripheral nerve function in patients with familial amyloid polyneuropathy after liver transplantation

BACKGROUND

The electrophysiological long-term effects of liver transplantation on peripheral nerve function in patients with familial amyloid polyneuropathy (FAP) have not been evaluated.

METHODS

Eight FAP patients with a proven ATTRVal30Met gene were observed for 10 years after liver transplantation. We performed repeated measurement of maximal motor nerve conduction velocity (MCV), distal latency, size of compound muscle action potential (CMAP) and maximal sensory nerve conduction velocity (SCV) in both the ulnar and tibial nerves. We also recorded the coefficients of variance in the R-R interval on the electrocardiogram (CV(R-R)).

RESULTS

Some autonomic symptoms subsided but motor and sensory symptoms 10 years after transplantation were either slightly improved or almost the same as before surgery in 7 of 8 patients. These 7 have returned to their previous social lives including their jobs. The MCV of the tibial nerve slightly improved, and other parameters of motor and sensory nerve function and CV(R-R) did not show any deterioration during the 10-year observation period.

CONCLUSIONS

Liver transplantation can halt the progression of peripheral neuropathy in FAP patients.