Design and simulation of losses in Ge/SiGe terahertz quantum cascade laser waveguides

The waveguide losses from a range of surface plasmon and double metal waveguides for Ge/Si_1-xGe_x THz quantum cascade laser gain media are investigated at 4.79 THz (62.6 μm wavelength). Double metal waveguides demonstrate lower losses than surface plasmonic guiding with minimum losses for a 10 μm thick active gain region with silver metal of 21 cm^-1 at 300 K reducing to 14.5 cm^-1 at 10 K. Losses for silicon foundry compatible metals including Al and Cu are also provided for comparison and to provide a guide for gain requirements to enable lasers to be fabricated in commercial silicon foundries. To allow these losses to be calculated for a range of designs, the complex refractive index of a range of nominally undoped Si_1-xGe_x with x = 0.7, 0.8 and 0.9 and doped Ge heterolayers were extracted from Fourier transform infrared spectroscopy measurements between 0.1 and 10 THz and from 300 K down to 10 K. The results demonstrate losses comparable to similar designs of GaAs/AlGaAs quantum cascade laser plasmon waveguides indicating that a gain threshold of 15.1 cm^-1 and 23.8 cm^-1 are required to produce a 4.79 THz Ge/SiGe THz laser at 10 K and 300 K, respectively, for 2 mm long double metal waveguide quantum cascade lasers with facet coatings.

Amyotrophic lateral sclerosis causes small fiber pathology

BACKGROUND AND PURPOSE

Our aim was to address the correlation between small fiber loss and amyotrophic lateral sclerosis (ALS) for disease onset, phenotype, genotype, duration, severity and sensory findings.

METHODS

Consecutive patients referred for suspected ALS were screened. Exclusion criteria were possible ALS and previous diagnosis or known risk factors for small fiber neuropathies. A sural nerve conduction study (NCS) was bilaterally recorded. The ALS functional rating scale revised was administered and loss of functions were calculated using the Milano-Torino staging (MITOS) system. Sensory symptoms and signs were recorded. Genetic analysis was performed by the next-generation sequencing approach. Skin biopsy was performed at the distal leg and intraepidermal nerve fiber (IENF) density was quantified in three non-consecutive sections following published guidelines. Findings were referred to age- and sex-adjusted normative values.

RESULTS

Fifty-seven patients including six with facial onset sensory and motor neuronopathy (FOSMN) were enrolled. Eight (15.7%) pure ALS patients and five (83%) FOSMN patients complained of sensory disturbances with different distributions. Sural NCS was normal in all except two patients. IENF density was reduced in 75.4% of pure ALS and 50% of FOSMN patients, without correlation with any disease features. IENF density was similarly reduced in bulbar (78.5%), flail limb (87.5%), pyramidal (100%), and spinal (68.2%) onset, as well as in genetic (83.3%) and sporadic (82%) ALS. There was no correlation with genotype, disease duration and severity.

CONCLUSIONS

Intraepidermal nerve fiber loss is a feature of most ALS patients. It does not correlate with onset, phenotype, course and severity of the disease, and cannot be considered a clinical or prognostic biomarker.

Supratentorial and pontine MRI abnormalities characterize recessive spastic ataxia of Charlevoix-Saguenay. A comprehensive study of an Italian series

BACKGROUND AND PURPOSE

The autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is an early-onset neurodegenerative disorder caused by mutations in the SACS gene. The disease, first described in Canadian families from Québec, is characterized by cerebellar ataxia, pyramidal tract involvement and peripheral neuropathy.

METHODS

Analysis of SACS gene allowed the identification of 14 patients with ARSACS from 13 unrelated Italian families. Clinical phenotype, gene mutations and magnetic resonance imaging (MRI) findings were analysed.

RESULTS

We found 16 novel SACS gene mutations, including a large in-frame deletion. The age at onset was in infancy, but one patient presented the first symptoms at age 32. Progression of the disease was variable, and increased muscle tone was mostly recognized in later stages. Structural MRI showed atrophy of the superior cerebellar vermis, a bulky pons exhibiting T2-hypointense stripes, identified as the corticospinal tract (CST), thinning of the corpus callosum and a rim of T2-hyperintensity around the thalami in 100% of cases. The presence of iron or other paramagnetic substances was excluded. Diffusion tensor imaging (DTI) revealed grossly over-represented transverse pontine fibres (TPF), which prevented reconstruction of the CST at this level (100% of cases). In all patients, significant microstructural alterations were found in the supratentorial white matter of forceps, cingulum and superior longitudinal fasciculus.

CONCLUSIONS

Our findings further enlarge the genetic spectrum of SACS mutations and widen the study of clinical phenotype. MRI characteristics indicate that pontine changes and supratentorial abnormalities are diagnostic. The over-representation of TPF on DTI suggests a developmental component in the pathogenesis of the disease.

POEMS syndrome: relapse after successful autologous peripheral blood stem cell transplantation

We report a patient with POEMS syndrome (Polyneuropathy, Organomegaly, Endocrinopathy, Monoclonal gammopathy, Skin changes) treated with high dose chemotherapy and auto-Peripheral Blood Stem Cell Transplantation (auto-PBSCT) who had a very good response with complete clinical remission. Seven years later, she relapsed and a new sclerotic bone lesion was found. To our knowledge, this is the first POEMS syndrome relapse after successful auto-PBSCT.

Movement-related desynchronization-synchronization (ERD/ERS) in patients with Unverricht-Lundborg disease

We studied changes in event-related desynchronization/synchronization (ERD/ERS) patterns in patients with Unverricht-Lundborg disease (ULD), presenting with prominent action myoclonus. We analyzed the movement-related ERD/ERS in alpha and beta frequency bands in 15 patients using self-paced finger extension as a motor paradigm and we compared the results with those obtained in 12 healthy volunteers. In all ULD patients, alpha- and beta-ERD regularly occurred with onset and location similar to that found in healthy controls, but the desynchronization of alpha activity was significantly greater than in controls (C3: -64.4+/-9.8% vs. -49.7+/-14.8%; p=0.004). Moreover, in the patients, both alpha- and beta-ERD spread toward frontal electrodes. In controls, the post-movement beta-ERS regularly occurred; it was absent in eight patients with severe action myoclonus, while, in seven patients with mild or moderate myoclonus, the beta-peak was significantly smaller with respect to that measured in controls (55.6+/-15.1% vs. 153.9+/-99.8%, p=0.006). The failure of beta-ERS well-correlated with motor impairment resulting from action myoclonus, whereas SSEPs and long-loop reflexes performed to detect signs of cortical hyperexcitability showed inconsistent changes. In ULD patients, ERD/ERS changes indicate an increased activation of motor cortex during movement planning and a great reduction of post-excitatory inhibition of motor cortex. The changes involving beta-ERS had a significant relationship with the functional disability in individual patients and might play a pathogenic role in the motor dysfunction.

Childhood-onset multifocal motor neuropathy with conduction blocks

Multifocal motor neuropathy (MMN) is an acquired disorder with onset in adulthood. The authors describe a patient with a slowly progressing distal upper limb motor neuropathy since age 6 years, in whom definite conduction blocks in upper limbs, outside common entrapment sites, and no sensory involvement were consistent with MMN. IV immunoglobulin treatment produced marked muscle strength improvement and conduction block disappearance. MMN diagnosis should also be considered in childhood.

Sequential antibodies to potassium channels and glutamic acid decarboxylase in neuromyotonia

A patient with thymoma-associated neuromyotonia and voltage-gated potassium channel (Kv1.2 and Kv1.6) antibodies by immunoprecipitation and rat brain immunolabeling was treated successfully with immunoadsorption and cyclophosphamide. Curiously, glutamic acid decarboxylase antibodies, absent at onset, appeared later. Stiff-person syndrome was absent, but fast blink reflex recovery suggested enhanced brainstem excitability. The range of antibodies produced in thymoma-associated neuromyotonia is richer, and the timing of antibody appearance more complex, than previously suspected.

Sensorimotor cortex excitability in Unverricht–Lundborg disease and Lafora body disease

Objective: To investigate whether Unverricht–Lundborg disease (ULD) and Lafora body disease (LBD) can be differentiated on the basis of their neurophysiologic profiles.

Methods: Somatosensory evoked potentials (SSEPs), long-loop reflexes (LLRs), and the influence of conditioning nerve stimulation on the motor potentials evoked by transcranial stimulation in 8 patients with LBD and 10 patients with ULD were investigated.

Results: Both groups showed sensorimotor cortex hyperexcitability, but their electrophysiologic profiles were different. Enlarged P25 to N33 SSEP components and enhanced LLRs were common in the ULD patients, whereas medium-latency “giant” SSEP components and less consistently enhanced LLRs were more frequently found in the patients with LBD. Cortical relay time was extremely brief in ULD but varied in LBD. Conditioning somatosensory stimuli differently affected motor cortex excitability, leading to early facilitation in ULD and delayed and prolonged facilitation in LBD.

Conclusions: Patients with Unverricht–Lundborg disease (ULD) and Lafora body disease (LBD) have different electrophysiologic profiles. The ULD findings point to an aberrant subcortical or cortical loop (possibly short-cutting the somatosensory cortex) that is involved in generating the prominent action myoclonus characterizing the disorder. The LBD findings highlight sustained hyperexcitability of the sensorimotor cortex in response to afferent stimuli, which fit with a more severe impairment of inhibitory mechanisms.

Progressive dysarthria: definition and clinical follow-up

Progressive dysarthria is a common sign of several degenerative disorders of the central nervous system; it may also be a distinct nosographic entity. We identified nine patients in which progressive dysarthria remained the sole neurological sign for at least 2 years after onset. At least a year after hospital admission, the following diagnoses were made: two cases of corticobasal degeneration, one of frontotemporal dementia, one of primary progressive aphasia, one of motor neuron disease (MND)-dementia, one of ALS, and one of ALS-aphasia. In the remaining two patients progressive dysarthria remained the only neurological sign at latest examination. We conclude that in most cases progressive dysarthria is the presenting sign of an established neurodegenerative disease (generally degenerative dementia or motor neuron disease), although the possibility that progressive dysarthria is a distinct entity cannot be excluded. To clarify this issue, studies (probably multicenter) on more patients with longer clinical follow-up and pathological confirmation are required.

Movement-activated myoclonus in genetically defined progressive myoclonic epilepsies: EEG-EMG relationship estimated using autoregressive models

OBJECTIVE

To study electroencephalography-electromyography (EEG-EMG) relationships in patients with different forms of progressive myoclonic epilepsies (PME).

METHODS

EEG-EMG auto-spectra, coherence and phase functions were estimated by means of bivariate and time varying autoregressive (AR) models in 15 patients: 8 with Unverricht-Lundborg, 4 with Lafora body disease, and 3 with sialidosis.

RESULTS

The coherence spectra of the EMG epochs including action myoclonus and contralateral frontocentral EEG derivations showed a main beta peak (average coherence: 0.60-0.79) in all patients, regardless of the type of PME. The time lag from cortex to muscle was 13.0-21.3 ms. Significantly, coherent gamma activity was consistently found only in the 3 patients with sialidosis; the most heterogeneous results were obtained in the patients with Lafora disease, who showed a more complex coherence profile. Periods of normal muscle contractions, which could be recorded in patients with Unverricht-Lundborg PME, were characterised by the presence of an EEG-EMG beta coherence peak on the same frequency as in the case of action myoclonus, but with a lower coherence value.

CONCLUSIONS

AR models were capable of describing EEG-EMG relationships in patients with PME, and indicated that coherent cortical and EMG beta oscillations are crucially involved in the generation of myoclonus. Moreover, they could detect the uneven spectral profiles characterising the different forms of PME.

Neurophysiological features in relation to clinical signs in clinically diagnosed corticobasal degeneration

We investigated the association between clinical and neurophysiological characteristics in patients with a clinical diagnosis of probable corticobasal degeneration (CBD), and searched for neurophysiological features supporting the diagnosis in life. Ten patients with clinically probable CBD underwent comprehensive neurological evaluation and brain MRI. Long latency reflexes (LLR), upper limb somatosensory (SEP) and motor evoked (MEP) potentials were recorded. The mini-mental state examination (MMSE), the phonemic verbal fluency test (PVFT) and the De Renzi ideomotor apraxia test were also performed. Polygraphic EEG was performed in the six patients with myoclonus. The SEP N30 frontal component was absent bilaterally in four patients, was absent on the left side in one, and had increased latency in other three. MEPs were abnormal in four patients (three had prolonged central motor conduction time, one of whom also had increased MEP threshold, and one had increased MEP threshold). All six patients with myoclonus had enhanced LLRs at rest, which were also of abnormally increased amplitude during motor activation; latencies were generally shorter than in classic cortical reflex myoclonus. On back-averaging, no EEG spikes time-locked to EMG activity were found in any myoclonus patient. Five patients were demented by MMSE, eight had ideomotor apraxia scores in the ideomotor apraxia range and five had defective verbal fluency. Brain MRI revealed asymmetric cortical atrophy in all patients, particularly evident frontoparietally. Neurophysiological techniques, particularly LLR, can assist CBD diagnosis especially in patients with myoclonus. Patients with evident parkinsonism had greater SEP N30 (frontal) abnormalities, while most patients with marked paresis had slower MEP times.

Cranial nerve involvement in CMT disease type 1 due to early growth response 2 gene mutation

Mutations in the gene coding for the Schwann cell transcription factor early growth response 2 (EGR2), which seems to regulate myelinogenesis and hindbrain development, have been observed in few cases of inherited neuropathy. The authors describe a unique combination of cranial nerve deficits in one member of a Charcot-Marie-Tooth 1 family carrying an EGR2 mutation (Arg381His). This finding further supports the role of EGR2 in cranial nerve development.

Chronic inflammatory demyelinating polyradiculoneuropathy: long-term course and treatment of 60 patients

The objective of this study was to assess the long-term course and treatment of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). We evaluated, according to a predefined protocol, a series of 60 CIDP patients who received a long-term course of steroids and immunosuppressants. Eighteen of them also had monoclonal gammopathy of undetermined significance (MGUS). Mean follow-up was 4.4 years and was similar for CIDP and CIDP-MGUS patients. At the end of the follow-up, improvement was ascertained in 60% of patients (69% CIDP, 39% CIDP-MGUS). Complete remission was achieved in 13%. Out of 26 patients receiving steroids as a monotherapy, 19 improved (73%). The following variables were predictive of a better outcome: female gender, younger age at onset, relapsing-remitting course, and absence of axonal damage at neurophysiologic study. In the multivariate analysis, younger age at onset and demyelination without axonal damage still retained an independent positive value.

Infantile neuroaxonal dystrophy: clinical spectrum and diagnostic criteria

OBJECTIVE

To present clinical, neurophysiologic, and neuroradiologic findings in 13 patients with infantile neuroaxonal dystrophy (INAD), focusing on aspects that assist early diagnosis.

BACKGROUND

Clinicopathologic diagnostic criteria for INAD were delineated by Aicardi and Castelein in 1979, but atypical cases are reported frequently and little is known of the diagnostic utility of MRI.

METHODS

The authors reviewed the clinical, neurophysiologic, and MRI findings of 13 patients who met the diagnostic criteria for INAD.

RESULTS

Symptoms onset was between 6 months and 2 years of age. In nine patients the clinical course was typical, with rapid motor and mental deterioration; in four patients progression was slower and the clinical picture was different. Electromyographic (EMG) signs of chronic denervation, fast rhythms on EEG and abnormal visual evoked potentials were observed in all patients during the disease course. Cerebellar atrophy with signal hyperintensity in the cerebellar cortex on T2-weighted images were the most characteristic MRI findings; hypointensity in the pallida and substantia nigra was also observed in two patients. alpha-N-acetyl-galactosaminidase activity on leukocytes was normal in the 10 patients tested.

CONCLUSIONS

EMG and MRI abnormalities are the earliest and most suggestive signs of INAD, which has a clinical and radiologic spectrum that is broader than reported previously.

Detection of hereditary neuropathy with liability to pressure palsies among patients with acute painless mononeuropathy or plexopathy

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder characterized by recurrent mononeuropathies or brachial plexopathies, commonly associated with a chromosome 17p11.2-12 deletion encompassing the peripheral myelin protein-22 (PMP22) gene. We tried to identify criteria distinguishing HNPP among patients with acute painless mononeuropathy/plexopathy. We investigated by pulsed-field gel electrophoresis the presence of the deletion in 27 patients with isolated or recurrent acute painless mononeuropathy or brachial plexopathy, and no obvious cause of neuropathy. Eight patients carried the deletion, whereas 19 had neither the deletion nor mutations in the PMP22 gene. Age at onset, presenting modality, precipitating events, and rate of recovery did not significantly differ in the two groups. Family history was informative for HNPP diagnosis in 3 cases only. HNPP patients more often showed recurrent episodes, brachial plexopathy, and clinical or electrophysiologic involvement of other nerves. Non-HNPP patients more frequently had peroneal palsy, recent weight loss, and normal electrophysiologic examination in other nerves. Signs of generalized neuropathy and evidence of disease in other family member are often subtle in HNPP and must be thoroughly investigated in patients with acute painless mononeuropathy/plexopathy.

Myoclonus in corticobasal degeneration

Five patients with unilateral myoclonus and a clinical diagnosis of corticobasal degeneration (CBD) were studied. All patients showed enhanced long-loop responses in their myoclonic arms without enlarged somatosensory potentials. The cortical relay time of the long-loop responses was studied in three patients, in two of whom it was < 2 ms, even in the nonmyoclonic arm. Myoclonus in CBD is probably related to an enhanced long-loop reflex whose pathway is unlikely to be the same as that in classic cortical reflex myoclonus.

Phenotypic heterogeneity in hereditary neuropathy with liability to pressure palsies associated with chromosome 17p11.2-12 deletion

Hereditary neuropathy with liability to pressure palsies (HNPP) is commonly associated with a 1.5-megabase deletion on chromosome 17p11.2-12. We analyzed the phenotypic expression of the deletion in 39 HNPP patients from 16 families carrying the deletion. Two-thirds of the individuals had episodes of acute mononeuropathy, often involving nerve territories of the upper limbs or brachial plexus; however, 41% of affected subjects were unaware of their disease, and 25% were almost or totally free of symptoms; one-third complained of chronic symptoms and four older patients had a picture of polyneuropathy. Electrophysiologic abnormalities differed among affected subjects, ranging from conduction abnormalities localized at common entrapment sites to diffuse conduction slowing, usually more evident at entrapment sites; patients from one family had preeminent proximal involvement. The spectrum of phenotypic expression of deletion-associated HNPP appears to be broader than previously thought. The prevalence of the disease is probably underestimated, and the availability of molecular diagnosis should increase disease detection.

Intrathecal immune activation in three patients with progressive myoclonic ataxia

Three patients displaying a clinical picture of progressively evolving multifocal action myoclonus and cerebellar ataxia showed a marked intrathecal immune activation, which was persistent over a 2- to 5-year time span in the two serially investigated patients. A thorough search for metabolic, toxic, infectious, or degenerative causes of myoclonus was unsuccessful. The presence of intrathecal immune activation in at least a subgroup of patients with the clinical features of progressive myoclonic ataxia suggests the possibility of immune-mediated damage within the central nervous system in this condition.

Serial evoked potentials in multiple sclerosis bouts. Relation to steroid treatment

Serial recordings of multimodal sensory (visual, acoustic and somatosensory) evoked potentials were made in 19 relapsing-remitting Multiple Sclerosis patients enrolled in a clinical trial designed to evaluate the efficacy of dexamethasone versus high- and low-dose methylprednisolone in acute multiple sclerosis bouts. Electrophysiological and clinical evaluations were performed at the onset of therapy and until 6 months after the end of treatment. Using an arbitrary Evoked Potentials score that takes into account both latency and waveform alterations, we found a positive correlation between evoked potentials and clinical disability scores. Furthermore, different electrophysiological profiles were detected in the three therapeutic subgroups. Evoked potentials may be useful for monitoring acute Multiple Sclerosis bouts and evaluating the effect of therapy.

Spasmodic dystonic laterocollis in familial cerebellar ataxia

The case of a woman affected by familial ataxia who developed marked spasmodic laterocollis is described. As this appears to be an uncommon association, it is worth reporting one more case.

Exteroceptive reflexes in dystonia: a study of the recovery cycle of the R2 component of the blink reflex and of the exteroceptive suppression of the contracting sternocleidomastoid muscle in blepharospasm and torticollis

The recovery cycle of the R2 component of the blink reflex and the exteroceptive suppression of EMG activity in the contracting sternocleidomastoid muscle produced by electrical stimulation of the supraorbital nerve were studied in normal subjects and in patients with either blepharospasm or torticollis. The latencies of the reflexes were normal, suggesting that the neural structures that mediated them were intact. However, the recovery of the R2 component of the blink reflex was enhanced in patients with either blepharospasm or torticollis. Also, the size of the exteroceptive suppression of the sternocleidomastoid muscle was reduced in both groups of patients. Our results are indicative of abnormalities of interneurons mediating exteroceptive reflexes in patients with craniocervical dystonia that are not restricted to the systems controlling the muscle involved in the dystonia.

Adult onset myoclonic Huntington's disease

A patient with adult onset Huntington's disease (HD) and prominent action myoclonus is described. Neither epileptiform activity nor electroencephalography (EEG) correlates of the movements was found. Unlike the case with most (nonmyoclonic) HD patients, centro-parietal components of somatosensory evoked potentials (SEPs) were well defined and a clear V2 response was found. Treatment with valproic acid greatly reduced myoclonus suggesting that the gamma-aminobutyric acid (GABA) system might be involved in the pathophysiology of myoclonus in HD.

Combined central and peripheral acute demyelination

We describe a patient with multiple sclerosis who had a bout of central demyelination associated with an acute inflammatory demyelinating polyneuropathy. The contemporary involvement of central and peripheral nervous system due to a demyelinating disease has been reported anecdotically in humans, and can be induced experimentally in animals. It may be sustained by a common pathogenetic factor.

HMSN III phenotype due to homozygous expression of a dominant HMSN II gene

We describe two siblings with hereditary motor and sensory neuropathy (HMSN) type III. Their parents were both affected with autosomal dominant axonal HMSN. The neuropathy in the siblings probably resulted from homozygous expression of the HMSN II gene. Together with other reports of homozygous HMSN I, this family suggests that HMSN III is heterogenous and encompasses the most severe homozygous expression of neuropathic genes.

Focal reflex myoclonus in corticobasal degeneration

Focal reflex myoclonus was observed in a patient clinically diagnosed as affected by corticobasal degeneration. Myoclonus was not preceded by a cortical discharge and contralateral parietal components of the somatosensory evoked potentials were reduced in amplitude. No simple pathophysiological mechanism can account for all cases of focal reflex myoclonus seen in clinical practice.

Surface-EMG analysis of rectus femoris in patients with spastic hemiparesis undergoing rehabilitation treatment

In the present study a surface-EMG investigation of the rectus femoris muscle was performed in patients with spastic hemiparesis before and after rehabilitation treatment. The EMG activity was detected during 50% of the maximum voluntary contraction by means of FFT automatic analysis; the mean power frequency (MPF) and the time-course of the frequencies of the surface-EMG signals showed significant changes after physiokinesitherapy. In hemiparetic patients a particular distribution of the frequencies of the surface-EMG signals towards the lowest values were observed. These findings could be related to the preferential atrophy of type II fibers which has been demonstrated in morphological studies. Furthermore the surface-EMG analysis after a period of rehabilitation treatment showed some significant modifications of MPF and time-course of the EMG signals. These changes corresponded to an improvement of the spasticity as evaluated by clinical rating-scale. This neurophysiological investigation seem to be a simple and reliable method for better evaluating some effects of the rehabilitation therapy.

Peripheral nerve conduction velocity in normal infants and children

Maximum motor conduction velocity of the median, ulnar and peroneal nerves and maximum sensory conduction velocity of the median nerve have been studied in 635 children, below 12 years of age, free from peripheral nervous system disease. The children fell into four age-group: from 0 to 1 year; from 1 to 3 years: from 3 to 6 years; from 6 to 12 years. No normal values were recorded for the sensory conduction velocity of the median nerve under the age of one year. The motor conduction velocity values significantly rise for the median and ulnar nerves up to 1 year, for the peroneal nerve up to 3 years. The sensory conduction velocity values of median nerve increase significantly up to 6 years.