Hereditary Neuropathy With Liability To Pressure Palsies Patients Research Articles

Anesthetic Considerations for Patients with Hereditary Neuropathy with Liability to Pressure Palsies: A Narrative Review.

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant demyelinating neuropathy characterized by an increased susceptibility to peripheral nerve injury from trauma, compression, or shear forces. Patients with this condition are unique, necessitating distinct considerations for anesthesia and surgical teams. This review describes the etiology, prevalence, clinical presentation, and management of HNPP and presents contemporary evidence and recommendations for optimal care for HNPP patients in the perioperative period. While the incidence of HNPP is reported at 7-16:100,000, this figure may be an underestimation due to underdiagnosis, further complicating medicolegal issues. With the subtle nature of symptoms associated with HNPP, patients with this condition may remain unrecognized during the perioperative period, posing significant risks. Several aspects of caring for this population, including anesthetic choices, intraoperative positioning, and monitoring strategy, may deviate from standard practices. As such, a tailored approach to caring for this unique population, coupled with meticulous preoperative planning, is crucial and requires a multidisciplinary approach.

Utility of Carpal Tunnel Release and Ulnar Decompression in CMT1A and HNPP.

Carpal and cubital tunnel syndrome (CTS, CuTS) are common among patients with hereditary neuropathy with liability to pressure-palsies (HNPP) and Charcot-Marie-Tooth type 1A (CMT1A) and may impact quality of life. We aimed to evaluate the utility of nerve decompression surgeries in these patients. Medical records were reviewed for patients with PMP22 mutations confirmed in Mayo Clinic laboratories from January 1999 to December 2020, who had CTS and CuTS and underwent surgical decompression. CTS occurred in 53.3% of HNPP and 11.5% of CMT1A, while CuTS was present in 43.3% of HNPP and 5.8% of CMT1A patients. CTS decompression occurred in 10-HNPP and 5-CMT1A patients, and CuTS decompression with/without transposition was performed in 5-HNPP and 1-CMT1A patients. In HNPP, electrodiagnostic studies identified median neuropathy at the wrist in 9/10 patients and ultrasound showed focal enlargements at the carpal and cubital tunnels. In CMT1A, median and ulnar sensory responses were all absent, and the nerves were diffusely enlarged. After CTS surgery, pain, sensory loss, and strength improved in 4/5 CMT1A, and 6/10 HNPP patients. Of clinical, electrophysiologic and ultrasound findings, only activity-provoked features significantly correlated with CTS surgical benefit in HNPP patients (odds ratio=117.0:95% confidence interval, 1.94 > 999.99, p=0.01). One CMT1A and one HNPP patient improved with CuTS surgery while 2 HNPP patients worsened. CTS symptom improvement post-surgery can be seen in CMT1A and (less frequent) in HNPP patients. CuTS surgery commonly worsened course in HNPP. Activity-provoked symptoms in HNPP best informed benefits from CTS surgery.

Candidate imaging biomarkers for PMP22-related inherited neuropathies.

ObjectiveCharcot–Marie–Tooth type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsy (HNPP) are caused by mutations to the peripheral myelin protein 22 (PMP22) gene. A need exists for sensitive and reliable biomarkers of progression and treatment response. Magnetic resonance imaging (MRI) metrics of nerve pathology and morphology were investigated for this purpose.MethodsMRI was performed at 3.0 T in the thigh of CMT1A (N = 11) and HNPP patients (N = 12) and controls (N = 23). Three potential imaging biomarkers of the sciatic nerve were investigated: 1) magnetization transfer ratio (MTR), which assays myelin content, and 2) cross‐sectional area (CSA) and 3) circularity, which assay morphological changes. Potential imaging biomarkers were compared across cohorts and assessed for relationships with disability in the legs (CMTESL), compound motor action potentials (CMAP), and motor conduction velocities (MCV). Inter‐rater reliability and test–retest repeatability were established for each imaging metric.ResultsSignificant differences in MTR, CSA, and circularity were observed in CMT1A relative to controls (p = 0.02, p < 0.001, and p = 0.003, respectively, via Wilcoxon rank‐sum tests). Differences were not observed in the HNPP cohort. Significant relationships were observed between MTR and clinical metrics (CMTESL: p = 0.003, CMAP: p = 0.03, MCV: p = 0.01); and between CSA and electrophysiology (CMAP: p = 0.002, MCV: p < 0.001). All metrics were reliable and repeatable with MTR the most reliable (intraclass correlation coefficient [ICC] >0.999, CV = 0.30%) and repeatable (ICC = 0.84, CV = 3.16%).InterpretationMTR, CSA, and circularity showed promise as reliable and sensitive biomarkers of CMT1A, but not HNPP. These warrant longitudinal investigation as response biomarkers in upcoming clinical trials of CMT1A, while other methods should be considered for HNPP.

Dosage effects of PMP22 on nonmyelinating Schwann cells in hereditary neuropathy with liability to pressure palsies

Focal thickening of the myelin sheath, also known as tomacula, is a characteristic pathological feature of patients with hereditary neuropathy with liability to pressure palsies (HNPP). However, a deeper understanding of the pathology underlying unmyelinated fibers and nonmyelinating Schwann cells is required. Electron microscopic examination of sural nerve biopsy specimens was performed for 14 HNPP patients with peripheral myelin protein 22 (PMP22) deletion, and their results were compared to 12 normal controls and 14 Charcot–Marie–Tooth disease type 1A (CMT1A) patients with PMP22 duplication. The number of unmyelinated axons in a single axon-containing nonmyelinating Schwann cell subunit in the HNPP group significantly increased compared with that in normal controls (1.99 ± 0.66 vs. 1.57 ± 0.52, p < 0.05). Conversely, these numbers significantly decreased in the CMT1A group compared with those in normal controls (1.16 ± 0.16, p < 0.05). Some unmyelinated axons in patients with HNPP were incompletely surrounded by the cytoplasm of Schwann cells, almost as if the Schwann cells failed to form mesaxons; such failure in mesaxon formation was not observed in normal controls or in patients with CMT1A. These findings suggest that PMP22 dosage affects nonmyelinating as well as myelinating Schwann cells.

Yield of the PMP22 deletion analysis in patients with compression neuropathies.

Hereditary neuropathy with liability to pressure palsies (HNPP) is a rare neuromuscular disorder, mostly caused by PMP22 deletion. To determine a yield of the genetic analysis of PMP22 gene deletion in patients with compression neuropathies. We included 112 patients with clinical suspicion of HNPP diagnosis. Nerve conduction studies (NCS) were performed for motor and sensory nerves bilaterally. Number of the PMP22 gene copies was determined using a real-time polymerase chain reaction (RT-PCR). PMP22 deletion was found in 34 (30.3%) patients. Patients with genetically confirmed HNPP had 12 years earlier disease onset compared to other patients with compression neuropathies (p < 0.01), more nerves affected during lifespan (5.5 ± 3.5 vs. 3.0 ± 2.0, p < 0.01) and at the time of referral (2.7 ± 2.5 vs. 2.0 ± 1.9, p < 0.05). HNPP patients had positive family history more frequently (p < 0.01). Foot deformities (pes cavus and hammertoe), symmetric muscle atrophy in lower legs and absent muscle reflexes in lower limbs were more common in HNPP patients. NCS abnormalities were also more common in HNPP group. Multiple linear regression analysis identified positive family history (β = + 0.35, p < 0.01) and decreased sensory conduction velocity in at least three sensory nerves (β = + 0.40, p < 0.01) as independent predictors of the PMP22 deletion. Among patients with compression neuropathies, those with a positive family history, earlier symptom onset and NCS abnormalities had a higher chance to have PMP22 deletion.

Quality of life in hereditary neuropathy with liability to pressure palsies is as impaired as in Charcot–Marie–Tooth disease type 1A

To date, only one study assessed quality of life (QoL) in patients with hereditary neuropathy with liability to pressure palsies (HNPP). We aimed to fill in this gap by investigating QoL in a cohort of patients with HNPP compared to Charcot-Marie-Tooth type 1A (CMT1A) patients, as well as to analyze sociodemographic and clinical features associated with QoL in HNPP. Eighteen genetically confirmed HNPP patients were age-and gender-matched with 18 CMT1A patients. SF-36 questionnaire was used to assess QoL. Medical Research Council (MRC) Sum Score, CMT Neuropathy Score (CMTNS), Overall Neuropathy Limitation Scale Score (ONLS), Falls Efficacy Score (FES), Visual Analog Pain Scale, Beck Depression Inventory (BDI) and Fatigue Severity Scale (FSS) were also used in our study. Although HNPP patients were less clinically impaired, no difference was observed in these two cohorts regarding SF-36 scores. Worse QoL in HNPP patients was associated with lower education (p < 0.01), physical work (p < 0.05), higher number of clinically affected nerves during the disease course (p < 0.01), worse MRC-SS score (p < 0.01), worse ONLS score (p < 0.01), and with more severe pain (p < 0.01), depression (p < 0.01), and fatigue (p < 0.01). Worse pain at the moment of testing appeared as a significant independent predictor of worse QoL in HNPP patients (β = -0.93, p < 0.001). QoL was similarly impaired in patients with HNPP and patients with CMT1A. We identified different factors associated with QoL in HNPP, and many of these factors are amenable to treatment which is of special interest in these still incurable disease.

Clinical, Electrophysiological and Molecular Features in Hereditary Neuropathy with Liability to Pressure Palsies

Introduction: Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal-dominant inherited peripheral neuropathy caused by deletions of the PMP22 gene (PMP22). It is classically characterized by episodes of repeated focal pressure neuropathies at common entrapment sites. Atypical forms are recognized and may occur in up to 56% of HNPP patients. The electrophysiological characteristics and the genetic studies are paramount for its diagnosis. We aim to describe clinical, electrophysiological and genetic features of a cohort of patients diagnosed with HNPP at a tertiary hospital. Methods: Retrospective study of patients with a confirmed diagnosis of HNPP, using descriptive statistics for their characterization. Results: Seventeen patients from 15 different families were included. Nine were males, and the overall mean age was 42.6 years-old. Age at first symptoms ranged from 3 to 46 years-old, with mean time until diagnosis of 9.3 years. Nine patients (53%) presented recurrent painless mononeuropathies or isolated focal compressive neuropathies, and eight patients (47%) had atypical presentation phenotypes, such as “Charcot-Marie-Tooth-like (CMT-like) and sensory neuropathy. Intra-familial clinical heterogeneity was observed. All patients showed nerve conduction slowing at common entrapment sites (median, ulnar and peroneal nerves), and signs of a more generalized peripheral nerve involvement were present in more than half of the patients. Fifteen patients carried the PMP22 gene deletion, and point mutations were present in two. Conclusion: Our cohort presents similar clinical characteristics to the literature description, with a significant proportion of patients with atypical presentations. The absence of clinical-electrophysiological correlation emphasise the importance of nerve conduction and genetic studies for the definite diagnosis of the disease.

Clinical and Molecular Characterization of PMP22 point mutations in Taiwanese patients with Inherited Neuropathy

Point mutations in the peripheral myelin protein 22 (PMP22) gene have been identified to cause demyelinating Charcot-Marie-Tooth disease (CMT) and hereditary neuropathy with liability to pressure palsy (HNPP). To investigate the mutation spectrum of PMP22 in Han-Chinese population residing in Taiwan, 53 patients with molecularly unassigned demyelinating CMT and 52 patients with HNPP-like neuropathy of unknown genetic causes were screened for PMP22 mutations by Sanger sequencing. Three point mutations were identified in four patients with demyelinating CMT, including c.256 C > T (p.Q86X) in two, and c.310delA (p.I104FfsX7) and c.319 + 1G > A in one each. One PMP22 missense mutation, c.124 T > C (p.C42R), was identified in a patient with HNPP-like neuropathy. The clinical presentations of these mutations vary from mild HNPP-like syndrome to severe infantile-onset demyelinating CMT. In vitro analyses revealed that both PMP22 p.Q86X and p.I104FfsX7 mutations result in truncated PMP22 proteins that are almost totally retained within cytosol, whereas the p.C42R mutation partially impairs cell membrane localization of PMP22 protein. In conclusion, PMP22 point mutations account for 7.5% and 1.9% of demyelinating CMT and HNPP patients with unknown genetic causes, respectively. This study delineates the clinical and molecular features of PMP22 point mutations in Taiwan, and emphasizes their roles in demyelinating CMT or HNPP-like neuropathy.

Neuropathy genetics

Charcot-Marie-Tooth disease (CMT) is the most frequent form of hereditary neuropathy. Three genes commonly causing CMT encode myelin-related proteins: peripheral myelin protein 22 (PMP22), myelin protein zero (MPZ) and connexin 32 (Cx32). PMP22 duplication causes mainly demyelinating phenotype, known as CMT1A, with slowed motor nerve conduction velocity (MCV). Two distinctive phenotypic subgroups are present in patients with MPZ mutations: one shows preserved MCV and exclusively axonal pathological features, while the other is exclusively demyelinating. Patients with Cx32 mutations show intermediate slowing of MCV. Hereditary neuropathy with liability to pressure palsies (HNPP) usually is associated with a deletion of PMP22, which represents a reciprocal product of CMT1A. Focal thickening of the myelin sheath, known as tomacula, is a characteristic pathological feature in HNPP. Motor conduction studies show age-associated deterioration of compound muscle action potentials in nerves vulnerable to repetitive compression (median, ulnar, and peroneal nerves), but not in others such as the tibial nerve, suggesting that irreversible axonal damage occurs at entrapment sites in motor nerves in HNPP patients. Familial amyloid polyneuropathy (FAP) is also an important hereditary neuropathy. Although FAP was originally reported in endemic foci of Portugal, Japan, and Sweden, recent progress in diagnostic techniques has revealed that late-onset form of this disease is widely prevalent beyond these conventional endemic foci. Clinicians should consider the possibility of FAP in patients presenting with neuropathy of undetermined etiology to avoid misdiagnosis.

Phenotypic spectrum of Charcot-Marie-Tooth disease due to LITAF/SIMPLE mutations: a study of 18 patients.

Charcot-Marie-Tooth (CMT) 1C due to mutations in LITAF/SIMPLE is a rare subtype amongst the autosomal dominant demyelinating forms of CMT. Our objective was to report the clinical and electrophysiological characteristics of 18 CMT1C patients and compare them to 20 patients with PMP22 mutations: 10 CMT1A patients and 10 patients with hereditary neuropathy with liability to pressure palsies (HNPP). Charcot-Marie-Tooth 1C patients were followed-up in referral centres for neuromuscular diseases or were identified by familial survey. All CMT1A and HNPP patients were recruited at the referral centre for neuromuscular diseases of Pitié-Salpêtrière Hospital. Two phenotypes were identified amongst 18 CMT1C patients: the classical CMT form ('CMT-like', 11 cases) and a predominantly sensory form ('sensory form', seven cases). The mean CMT neuropathy score was 4.45 in CMT1C patients. Motor nerve conduction velocities in the upper limbs were significantly more reduced in CMT1A than in CMT1C patients. On the other hand, the motor nerve conduction velocity of the median nerve was significantly lower in CMT1C compared to the HNPP group. Distal motor latency was significantly more prolonged in CMT1A patients compared to the CMT1C and HNPP groups, the latter two groups having similar distal motor latency values. Molecular analysis revealed five new LITAF/SIMPLE mutations (Ala111Thr, Gly112Ala, Trp116Arg, Pro135Leu, Arg160Cys). Our study delineates CMT1C as mostly a mild form of neuropathy, and gives clinical and electrophysiological clues differentiating CMT1C from CMT1A and HNPP. Delineating phenotypes in CMT subtypes is important to orient molecular diagnosis and to help to interpret complex molecular findings.

Afferent Visual Pathway Affection in Patients with PMP22 Deletion-Related Hereditary Neuropathy with Liability to Pressure Palsies.

BackgroundThe PMP22 gene encodes a protein integral to peripheral myelin. Its deletion leads to hereditary neuropathy with liability to pressure palsies (HNPP). PMP22 is not expressed in the adult central nervous system, but previous studies suggest a role in CNS myelin development. The objective of this study was to identify potential structural and functional alterations in the afferent visual system in HNPP patients.MethodsTwenty HNPP patients and 18 matched healthy controls (HC) were recruited in a cross-sectional study. Participants underwent neurological examination including visual acuity, visual evoked potential (VEP) examination, optical coherence tomography (OCT), and magnetic resonance imaging with calculation of brain atrophy, regarding grey and white matter, and voxel based morphometry (VBM), in addition answered the National Eye Institute’s 39-item Visual Functioning Questionnaire (NEI-VFQ). Thirteen patients and 6 HC were additionally examined with magnetic resonance spectroscopy (MRS).ResultsAll patients had normal visual acuity, but reported reduced peripheral vision in comparison to HC in the NEI-VFQ (p = 0.036). VEP latency was prolonged in patients (P100 = 103.7±5.7 ms) in comparison to healthy subjects (P100 = 99.7±4.2 ms, p = 0.007). In OCT, peripapillary retinal nerve fiber layer thickness RNFL was decreased in the nasal sector (90.0±15.5 vs. 101.8±16.5, p = 0.013), and lower nasal sector RNFL correlated with prolonged VEP latency (Rho = -0.405, p = 0.012). MRS revealed reduced tNAA (731.4±45.4 vs. 814.9±62.1, p = 0.017) and tCr (373.8±22.2 vs. 418.7±31.1, p = 0.002) in the visual cortex in patients vs. HC. Whole brain volume, grey and white matter volume, VBM and metabolites in a MRS sensory cortex control voxel did not differ significantly between patients and HC.ConclusionPMP22 deletion leads to functional, metabolic and macro-structural alterations in the afferent visual system of HNPP patients. Our data suggest a functional relevance of these changes for peripheral vision, which warrants further investigation and confirmation.

Laryngeal and phrenic nerve involvement in a patient with hereditary neuropathy with liability to pressure palsies (HNPP)

Lower cranial and phrenic nerve involvement is exceptional in hereditary neuropathy with liability to pressure palsies (HNPP). Here we report the occurrence of reversible laryngeal and phrenic nerve involvement in a patient with HNPP. The patient recalled several episodes of reversible weakness and numbness of his feet and hands since the age of 30 years. His medical history was uneventful, apart from chronic obstructive pulmonary disease (COPD). At age 44, following severe weight loss, he presented with progressive dysphonia and hoarseness. EMG of cricoarytenoid and thyroarytenoid muscles and laryngeal fibroscopy confirmed vocal cord paralysis. These speech disturbances gradually regressed. Two years later, he reported rapidly worsening dyspnea. Electroneurography showed increased distal latency of the right phrenic nerve and diaphragm ultrasonography documented reduced right hemi-diaphragm excursion. Six months later and after optimization of CODP treatment, his respiratory function had improved and both phrenic nerve conduction and diaphragm excursion were completely restored. We hypothesize that chronic cough and nerve stretching in the context of CODP, together with severe weight loss, may have triggered the nerve paralysis in this patient. Our report highlights the need for optimal management of comorbidities such as CODP as well as careful control of weight in HNPP patients to avoid potentially harmful complications.

Analysis of PMP22 duplication and deletion using a panel of six dinucleotide tandem repeats.

Charcot-Marie-Tooth type 1A (CMT1A) is the most common type of hereditary motor and sensory neuropathies (HMSN), caused by the duplication of the 17p11.2 region that includes the PMP22 gene. Reciprocal deletion of the same region is the main cause of hereditary neuropathy with liability to pressure palsies (HNPP). CMT1A accounts for approximately 50% of HMSN patients. Diagnostics of CMT1A and HNPP are based on quantitative analysis of the affected region or RFLP detection of breakage points. The aim of this study was to improve the sensitivity and efficiency of CMT1A and HNPP genetic diagnostics by introducing analysis of six STR markers (D17S261-D17S122-D17S839-D17S1358-D17S955-D17S921) spanning the duplicated region. Forty-six CMT1A and seven HNPP patients, all genetically diagnosed by RFLP analysis, were tested for duplication or deletion using six STR markers. In all CMT1A and HNPP patients, microsatellite analysis comprising six STR markers confirmed the existence of a duplication or deletion. In 89% (41/46) CMT1A patients the confirmation was based on detecting three alleles on at least one locus. In the remaining 11% (5) CMT1A patients, duplication was also confirmed based on two peaks with clear dosage difference for at least two different markers. All HNPP patients (7/7) displayed only one allele for each analyzed locus. Microsatellite analysis using six selected STR loci showed a high level of sensitivity and specificity for genetic diagnostics of CMT1A and HNPP. The results here strongly suggest STR marker analysis as a method of choice in PMP22 duplication/deletion testing.

DTI Study of Cerebral Normal-Appearing White Matter in Hereditary Neuropathy With Liability to Pressure Palsies (HNPP).

The majority of previous studies on hereditary neuropathy with liability to pressure palsies (HNPP) were focused on peripheral nerves, whereas cerebral alterations in HNPP have been less attended to. In this work, Diffusion tensor imaging (DTI) was used to detect the changes in WM, especially in the normal-appearing white matter (NAWM) in HNPP patients for its sensitivity in probing the microstructure of WM, the sensitive metric was searched for probing cerebral alterations and the regional distribution of cerebral abnormalities was identified. Twelve HNPP patients and 12 age- and gender-matched healthy controls underwent the conventional MRI, DTI scan, and electrophysiological examination. The conventional MRI images were first analyzed to identify abnormal intense regions and the NAWM regions. NAWM refers to the white matter regions that do not include the lesions on conventional MRI. The apparent diffusion coefficient and fractional anisotropy (FA) values of the NAWM were then measured and compared between patient and control groups. The sensitivity and specificity of 3 methods and the cerebral regional distribution of MR signal abnormalities were further analyzed. Hyperintense foci were observed on T2 weighted image and fluid attenuated inversion recovery images in 6 patients. Compared to the controls, FA values of the patients were significantly lower in bilateral frontal, orbitofrontal, and temporal NAWMs; whereas the electrophysiological examination results of patients and controls exhibited no statistically significant difference. The sensitivity of FA value was higher than that of electrophysiological examination and conventional MRI. The majority of abnormal signals on conventional MRI images and abnormal FA values were located in the frontal and temporal lobes. The results of our study show cerebral WM changes in HNPP patients. FA value in DTI has been shown to be sensitive to the cerebral microstructural changes in HNPP. The frontal lobe is the predilection site that is most involved in HNPP.

Characteristic features of hereditary neuropathy with liability to pressure palsy (HNPP) presenting with brachial plexopathy in soldiers

A brachial plexus lesion is not common in hereditary neuropathy with liability to pressure palsy (HNPP). We report the clinical and electrodiagnostic features of young soldiers with HNPP presenting with brachial plexopathy. By reviewing 2year medical records from Korean military hospitals, we identified soldiers with brachial plexus lesions. Among them, patients diagnosed with HNPP were determined and clinical and electrophysiological findings were compared between HNPP and non-HNPP patients with a brachial plexus lesion. Thirteen patients (6.8%) were diagnosed with HNPP among 189 patients with a brachial plexus lesion. Push-ups, as either a punishment or an exercise, was the most frequent preceding event in HNPP patients (76.9%), whereas it was rare in non-HNPP patients. The distal motor latency of the median nerve showed the highest sensitivity (90.9%) and specificity (100%) for HNPP in patients with a brachial plexus lesion. In conclusion, HNPP should be suspected in patients with brachial plexopathy if brachial plexopathy develops after push-ups or if the distal motor latency of median nerves is prolonged.

Axonal dysfunction, dysmyelination, and conduction failure in hereditary neuropathy with liability to pressure palsies.

Patients with hereditary neuropathy with liability to pressure palsies (HNPP) manifest with episodes of focal paresis when exposed to mechanical stress, although the basis for vulnerability to conduction block remains relatively unexplained. Axonal excitability techniques were utilized to provide insights into pathophysiological mechanisms in 13 HNPP patients, stimulating median motor and sensory axons at the wrist. In HNPP, distal latencies were prolonged, and motor and sensory amplitudes were reduced. Threshold was increased. Depolarizing and hyperpolarizing electrotonus was greater, and resting current-threshold slope was reduced. There were greater threshold changes in superexcitability, and refractoriness was decreased. Taken together, excitability testing in patients with HNPP established axonal hyperpolarization in both motor and sensory axons that may be attributable to changes in nerve architecture. In turn, the hyperpolarized resting membrane potential in HNPP may be a major predisposing factor for development of conduction block with mechanical stresses.

Clinical, electrophysiological and magnetic resonance findings in a family with hereditary neuropathy with liability to pressure palsies caused by a novel PMP22 mutation

Hereditary neuropathy with liability to pressure palsies (HNPP) is a disorder mainly caused by a 1.5-Mb deletion at 17p11.2-12 (and in some rare cases by point mutations) and clinically associated with recurrent painless palsies. Here, we performed electrophysiological (motor, sensory and terminal latency index), MRI and genetic studies in a family referred for ulnar neuropathy with pain.Surprisingly, we found typical neurophysiological features of HNPP (prolongation of distal motor latencies and diffuse SNCV slowing with significant slowing of motor nerve conduction velocities). Besides, the proband presented conduction block in left ulnar, left median and both peroneal nerves. MRI findings were consistent with an underlying neuropathy. Molecular studies identified a novel frameshift mutation in PMP22 confirming the diagnosis of HNPP.Our data suggest that neurophysiological studies are essential to characterize underdiagnosed HNPP patients referred for peripheral neuropathy. Our experience shows that MRI could be a complementary tool for the diagnosis of these patients.

Electrophysiological comparison between males and females in HNPP

Some evidences highlighted a higher clinical expression of hereditary neuropathy with liability to pressure palsy (HNPP) in males, and a higher load of traumatic nerve injuries due to different occupational activity has been invoked to explain this observation. It is unknown whether this increased clinical impairment corresponds to a greater electrophysiological involvement. Thus, we compared clinical and electrophysiological features between men and women in a large cohort of HNPP patients. Nerve palsies and electrophysiological abnormalities were more frequent in men, and electrophysiological findings which differentiated males from females did not show any age-related worsening. In conclusion, our findings showed a higher clinical and electrophysiological involvement in males which does not seem related to different cumulative nerve damage over time. We believe that the higher disease expression may increase the chance to detect the disease in males and, thereby, to underestimate the HNPP diagnosis in females.

Neurophysiological diagnosis of hereditary neuropathy with liability to pressure palsies

Objective To explore the neurophysiological properties of hereditary neuropathy with liability to pressure palsies(HNPP),so as to provide evidence for the diagnosis of HNPP.Methods Three families(8 individuals) with clinically affected and asymptomatic HNPP patients underwent routine electrodiagnostic tests,including median,ulnar,radial,tibial and proneal motor and sensory nerve conduction,and the results were compared with those of 30 healthy subjects.Results(1)Prolongation of the distal nerve conduction latencies was the most seen abnormality(92.1%),mainly found in the median and common peroneal nerves,including those with and without symptoms.(2)The rate of motor nerve conduction slowing was 63.2%,mostly seen in the median and common peroneal nerves.(3)The rate of sensory nerve conduction slowing was 89.6%,mostly affecting the sural and median nerves.(4)The conduction block of the ulnar nerve at the elbow was more commonly seen than that of the proneal nerve at the fibular head.Conclusion Neurophysiological examination is a noninvasive,fast,simple and accurate diagnosis way for clinically suspected HNPP patients,and it can be used for screening the family members of HNPP patients and for prevention of HNPP.

P3.17 The extremes of the clinical spectrum of CMT1A and HNPP patients: Phenotypic characteristics

Charcot-Marie-Tooth disease type 1A (CMT1A) and hereditary neuropathy with liability to pressure palsies (HNPP) are autosomal dominant peripheral neuropathies caused by copynumber variation of the PMP22 gene. The clinical variability of these disorders is wide, between as well as within families. This variability suggests the presence of modifiers. We previously identified cases of double trouble (the presence of two mutations in CMT-related genes) in severely affected patients, i.e. known CMT genes can act as modifiers.