Francesca Camozzi

The diagnostic criteria for small fibre neuropathy: from symptoms to neuropathology

Small fibre neuropathy (SFN), a condition dominated by neuropathic pain, is frequently encountered in clinical practise either as prevalent manifestation of more diffuse neuropathy or distinct nosologic entity. Aetiology of SFN includes pre-diabetes status and immune-mediated diseases, though it remains frequently unknown. Due to their physiologic characteristics, small nerve fibres cannot be investigated by routine electrophysiological tests, making the diagnosis particularly difficult. Quantitative sensory testing (QST) to assess the psychophysical thresholds for cold and warm sensations and skin biopsy with quantification of somatic intraepidermal nerve fibres (IENF) have been used to determine the damage to small nerve fibres. Nevertheless, the diagnostic criteria for SFN have not been defined yet and a ‘gold standard’ for clinical practise and research is not available. We screened 486 patients referred to our institutions and collected 124 patients with sensory neuropathy. Among them, we identified 67 patients with pure SFN using a new diagnostic ‘gold standard’, based on the presence of at least two abnormal results at clinical, QST and skin biopsy examination. The diagnosis of SFN was achieved by abnormal clinical and skin biopsy findings in 43.3% of patients, abnormal skin biopsy and QST findings in 37.3% of patients, abnormal clinical and QST findings in 11.9% of patients, whereas 7.5% patients had abnormal results at all the examinations. Skin biopsy showed a diagnostic efficiency of 88.4%, clinical examination of 54.6% and QST of 46.9%. Receiver operating characteristic curve analysis confirmed the significantly higher performance of skin biopsy comparing with QST. However, we found a significant inverse correlation between IENF density and both cold and warm thresholds at the leg. Clinical examination revealed pinprick and thermal hypoesthesia in about 50% patients, and signs of peripheral vascular autonomic dysfunction in about 70% of patients. Spontaneous pain dominated the clinical picture in most SFN patients. Neuropathic pain intensity was more severe in patients with SFN than in patients with large or mixed fibre neuropathy, but there was no significant correlation with IENF density. The aetiology of SFN was initially unknown in 41.8% of patients and at 2-year follow-up a potential cause could be determined in 25% of them. Over the same period, 13% of SFN patients showed the involvement of large nerve fibres, whereas in 45.6% of them the clinical picture did not change. Spontaneous remission of neuropathic pain occurred in 10.9% of SFN patients, while it worsened in 30.4% of them.

Alpha-lipoic acid prevents mitochondrial damage and neurotoxicity in experimental chemotherapy neuropathy

The study investigates if alpha-lipoic acid is neuroprotective against chemotherapy induced neurotoxicity, if mitochondrial damage plays a critical role in toxic neurodegenerative cascade, and if neuroprotective effects of alpha-lipoic acid depend on mitochondria protection. We used an in vitro model of chemotherapy induced peripheral neuropathy that closely mimic the in vivo condition by exposing primary cultures of dorsal root ganglion (DRG) sensory neurons to paclitaxel and cisplatin, two widely used and highly effective chemotherapeutic drugs. This approach allowed investigating the efficacy of alpha-lipoic acid in preventing axonal damage and apoptosis and the function and ultrastructural morphology of mitochondria after exposure to toxic agents and alpha-lipoic acid. Our results demonstrate that both cisplatin and paclitaxel cause early mitochondrial impairment with loss of membrane potential and induction of autophagic vacuoles in neurons. Alpha-lipoic acid exerts neuroprotective effects against chemotherapy induced neurotoxicity in sensory neurons: it rescues the mitochondrial toxicity and induces the expression of frataxin, an essential mitochondrial protein with anti-oxidant and chaperone properties. In conclusion mitochondrial toxicity is an early common event both in paclitaxel and cisplatin induced neurotoxicity. Alpha-lipoic acid protects sensory neurons through its anti-oxidant and mitochondrial regulatory functions, possibly inducing the expression of frataxin. These findings suggest that alpha-lipoic acid might reduce the risk of developing peripheral nerve toxicity in patients undergoing chemotherapy and encourage further confirmatory clinical trials.

Expression of capsaicin receptor immunoreactivity in human peripheral nervous system and in painful neuropathies

Abstract  We describe the expression of the capsaicin receptor (TRPV1) in human peripheral nervous system (PNS) and its changes in sural nerve and skin nerve fibers of patients with painful neuropathy. Dorsal root ganglion (DRG), root, and spinal cord autopsy specimens from subjects without PNS diseases were immunoassayed with anti‐TRPV1 antibodies. Bright‐field and confocal microscope studies using anti‐TRPV1, protein gene product 9.5 (PGP 9.5), and unique‐β‐tubulin (TuJ1) antibodies were performed in skin biopsies from 15 healthy subjects and 10 painful neuropathies. The density of intraepidermal nerve fiber (IENF) labeled by each antibody was quantified. Sural nerve biopsies from three patients with painful, one patient with nonpainful diabetic neuropathy, and two patients with multifocal motor neuropathy used as controls were immunoassayed with anti‐TRPV1 antibodies and investigated by immunoelectron microscopy. TRPV1 strongly labeled laminae I and II of dorsal horns, most small‐size and some medium‐size DRG neurons, and small‐diameter axons of dorsal roots. In sural nerve, TRPV1 was expressed within the cytoplasm of most unmyelinated and some small myelinated axons, in the muscular lamina of epineural vessels, and in the endothelium of endoneurial vessels. The density of IENF labeled by TRPV1, PGP 9.5, and TuJ1 did not differ. TRPV1 colocalized with TuJ1 in all IENF and dermal nerve bundles. Painful neuropathies showed a diffuse loss of TRPV1‐positive axons both in the sural nerve and in the skin. Our findings demonstrated that TRPV1 is normally expressed throughout the nociceptive pathway of PNS and that TRPV1‐positive peripheral nerve fibers degenerate in painful neuropathies.

Testosterone derivatives are neuroprotective agents in experimental diabetic neuropathy.

Abstract.In this study we have assessed the effect of testosterone (T), dihydrotestosterone (DHT) and 5αandrostan-3α, 17β-diol (3α-diol) therapies on diabetic neuropathy. Diabetes was induced in adult male rats by the injection of streptozotocin and resulted in decreased T and increased 3α-diol levels in plasma and in decreased levels of pregnenolone and DHT in the sciatic nerve. Moreover, a reduced expression of the enzyme converting Tinto DHT (i.e., the 5α-reductase) also occurs at the level of sciatic nerve, suggesting that the decrease of DHT levels could be due to an impairment of this enzyme. Chronic treatment for 1 month with DHT or 3α-diol increased tail nerve conduction velocity and partially counteracted the increase of thermal threshold induced by diabetes. Treatment with DHT increased tibial Na+,K+-ATPase activity and the expression of myelin protein P0 in the sciatic nerve.DHT, 3α-diol and T reversed the reduction of intra-epidermal nerve fiber density induced by diabetes. These observations indicate that T metabolites can reverse behavioral, neurophysiological, morphological and biochemical alterations induced by peripheral diabetic neuropathy.

Docetaxel-induced peripheral neuropathy: protective effects of dihydroprogesterone and progesterone in an experimental model

Abstract  Peripheral neurotoxicity is a frequent complication limiting docetaxel chemotherapy in patients with cancer. We developed an experimental model that closely mimics the course of neuropathy in patients, aiming to investigate both the mechanisms of neurotoxicity at biochemical, functional and morphological levels and the potential neuroprotective role of neuroactive steroids. We demonstrated that treatment with dihydroprogesterone (DHP) or progesterone (P) counteracts docetaxel‐induced neuropathy, preventing nerve conduction and thermal threshold changes, and degeneration of skin nerves in the foodpad. Neuroactive steroids also counteract the changes in gene expression of several myelin proteins and calcitonin gene‐related peptide induced by docetaxel in sciatic nerve and lumbar spinal cord, respectively. Most nerve abnormalities observed during the treatment with docetaxel spontaneously recovered after drug withdrawal, similarly to what occurs in patients. However, results of midterm follow‐up experiments indicated that animals cotreated with DHP or P have a faster recovery of the neuropathy compared with docetaxel‐treated rats. Our study confirmed that neuroactive steroids exert a protective effect on peripheral nerves at different levels, suggesting that they might represent a new therapeutic frontier for patients with chemotherapy‐induced neuropathy.

Altered peripheral myelination in mice lacking GABAB receptors

Emerging evidence implicates gamma-aminobutyric acid type B (GABA(B)) receptors in peripheral nervous system (PNS) functions. In order to elucidate which biochemical, morphological and functional parameters of peripheral nerve fibers depend on GABA(B) receptors we studied GABA(B1)-deficient mice, which are devoid of functional GABA(B) receptors. Here, we show that GABA(B1)-deficient mice exhibit morphological and molecular changes in peripheral myelin, including an increase in the number of irregular fibers and increases in the expression levels of the myelin proteins PMP22 and P0. Moreover, the number of small myelinated fibers and small neurons of the lumbar dorsal root ganglia is higher in GABA(B1)-deficient mice than in wild-type littermates. We further show that GABA(B1)-deficient mice exhibit gait alterations and reduced allodynia. In summary, our findings implicate GABA(B) receptors in the PNS myelination process and raise the possibility that PNS alterations contribute to the sensory phenotypes of GABA(B1)-deficient mice.

Burning Tongue and Burning Tip : The Diagnostic Challenge of the Burning Mouth Syndrome

ObjectiveTo investigate the clinical features of burning mouth syndrome (BMS) in a large cohort of patients and to correlate them with the results of tongue biopsy. MethodsWe screened 98 patients complaining of oral burning pain for at least 6 months. Forty-two patients were excluded after screening for contact sensitivity to dental materials, food allergies, tongue injuries, malignancies, connective tissue and metabolic disorders, oral infectious diseases, vitamin deficiencies, and other systemic diseases known to cause neuropathy. Fifty-six patients underwent neurologic examination and assessment of pain intensity, depression, anxiety, quality of sleep, and quality of life. Tongue biopsy with the quantification of epithelial nerve fibers (ENF) was performed in 51 patients. ResultsCompared with 9 healthy participants (4.13±1.85 SD), epithelial innervation density was significantly reduced in 38 patients (1.35±1.46 SD; P<0.0001) and normal in 13 patients (6.1±2.19 SD). The clinical features differed in the two groups: patients with reduced ENF density complained of pain in the whole tongue, lips, hard palate, and alveolar ridges, reported dysgeusia and xerostomia in 29% of cases (P<0.001), and 24% of them were depressed. Patients with normal innervation complained of pain on the tip of the tongue, reported dysgeusia and xerostomia in 7.7% of cases, and 54% of them were depressed (P<0.017). DiscussionThe diagnostic criteria for BMS are not defined yet and the relationship with depression and anxiety is debated. We proposed a biopsy-supported approach for the diagnosis. Our study shows that BMS can present with two distinct clinical pictures and that tongue biopsy can contribute to the assessment of the diagnosis. Mood disorders occur frequently and should be considered when approaching patients and treatment options. These observations could help physicians in identifying patients with BMS and addressing them with the appropriate diagnostic work-up and treatment.

Short‐ and intermediate‐term efficacy of buprenorphine TDS in chronic painful neuropathies

Abstract  Buprenorphine is a potent opioid available as a transdermal delivery system (TDS) formulation. This open‐label study investigated its safety, tolerability, and efficacy in 30 patients with chronic painful neuropathy. Subjects with visual analogue scale (VAS) score ≥5 under stable analgesic treatment were entered. The starting dosage of 35 μg/h was increased up to 70.0 μg/h in case of unsatisfactory pain control as assessed by fortnightly visits. The primary endpoint was the number of patients achieving at least 30% pain relief at day 42 visit. Treatment was safe over the study period. Nine patients dropped out for side effects, mostly nausea and daily sleepiness. Buprenorphine TDS was well tolerated in 21 patients. Thirteen patients achieved >30% of pain relief at day 42 visit. Five patients needed to increase the dosage to 52.5 μg/h. Eight patients did not meet the primary outcome, but none allowed increasing the dosage to 70 μg/h, and four patients withdrew consent to continue the study before day 42 visit because of a ‘fear to become addicted,’ although 40% had obtained VAS reduction. In our study, which needs to be confirmed by a controlled trial, buprenorphine TDS induced clinically meaningful pain relief in about 40% of patients with chronic painful neuropathy, suggesting its use as a third‐line treatment.