Clinical Spectrum and Prognosis in Patients With Acute Nutritional Axonal Neuropathy

BACKGROUND AND OBJECTIVES

To describe the clinical, micronutrient, and electrophysiologic spectrum and prognosis in patients with acute nutritional axonal neuropathy (ANAN).

METHODS

ANAN patients were identified between 1999 and 2020 by retrospective review of our EMG database and electronic health records, and categorized on clinical and electrodiagnostic grounds as pure sensory, sensorimotor, or pure motor; and by risk factor (alcohol use disorder, bariatric surgery, or anorexia). Laboratory abnormalities were recorded including thiamine, vitamin B6, B12 and E, folate and copper. Ambulatory and neuropathic pain status at last follow up was recorded.

RESULTS

Of 40 ANAN patients, 21 had alcohol use disorder, 10 were anorexic, and 9 had recently undergone bariatric surgery. Their neuropathy was pure sensory in 14 (7 with low thiamine), sensorimotor in 23 (8 with low thiamine), and pure motor in 3 (1 with low thiamine). Vitamin B1 was most commonly low (85%), followed by vitamin B6 (77%) and folate (50%). The risk factor and neuropathy type was not associated with a particular micronutrient deficiency. Of the 37 patients who were seen in follow-up, only 13 (35%) were walking independently, and only 8 (22%) were pain free at the last follow-up visit at a mean of 22 months (range: 2-88 months) from onset.

DISCUSSION

The spectrum of ANAN is wide ranging from: 1) a pure sensory neuropathy with areflexia, limb and gait ataxia, neuropathic pain and unevocable sensory responses to 2) a motor axonal neuropathy with low-amplitude motor responses without conduction slowing, block, or dispersion, and 3) a mixed sensorimotor axonal polyneuropathy. Specific micronutrient deficiencies or risk factors do not predict neuropathy subtype. The sub-group of ANAN patients with documented thiamine deficiency also range from pure sensory to pure motor, and only a minority have Wernicke's encephalopathy. We do not know whether co-existent micronutrient deficiencies may help explain the wide clinical spectrum of thiamine-deficient ANAN. The prognosis of ANAN is guarded due to residual neuropathic pain and slow recovery of independent ambulation. Therefore, early recognition of patients at risk is important.

Long Exercise Test in Periodic Paralysis: A Bayesian Analysis

INTRODUCTION

The long exercise test (LET) is used to assess the diagnosis of periodic paralysis (PP), but LET methodology and normal "cutoff" values vary.

METHODS

To determine optimal LET methodology and cutoffs, we reviewed LET data (abductor digiti minimi motor response amplitude, area) from 55 patients with PP (32 genetically definite) and 125 controls. Receiver operating characteristic curves were constructed, and area under the curve (AUC) was calculated to compare (1) peak-to-nadir versus baseline-to-nadir methodologies and (2) amplitude versus area decrements. Using bayesian principles, we calculated optimal cutoff decrements that achieved 95% posttest probability of PP for various pretest probabilities (PreTPs).

RESULTS

AUC was highest for peak-to-nadir methodology and equal for amplitude and area decrements. For PreTP ≤ 50%, optimal decrement cutoffs (peak-to-nadir) were > 40% (amplitude) or > 50% (area).

DISCUSSION

For confirmation of PP, our data endorse the diagnostic utility of peak-to-nadir LET methodology using 40% amplitude or 50% area decrement cutoffs for PreTP ≤50%. Muscle Nerve 59:47-54, 2019.

Acute nutritional axonal neuropathy

INTRODUCTION

This study describes clinical, laboratory, and electrodiagnostic features of a severe acute axonal polyneuropathy common to patients with acute nutritional deficiency in the setting of alcoholism, bariatric surgery (BS), or anorexia.

METHODS

Retrospective analysis of clinical, electrodiagnostic, and laboratory data of patients with acute axonal neuropathy.

RESULTS

Thirteen patients were identified with a severe, painful, sensory or sensorimotor axonal polyneuropathy that developed over 2-12 weeks with sensory ataxia, areflexia, variable muscle weakness, poor nutritional status, and weight loss, often with prolonged vomiting and normal cerebrospinal fluid protein. Vitamin B6 was low in half and thiamine was low in all patients when obtained before supplementation. Patients improved with weight gain and vitamin supplementation, with motor greater than sensory recovery.

DISCUSSION

We suggest that acute or subacute axonal neuropathy in patients with weight loss or vomiting associated with alcohol abuse, BS, or dietary deficiency is one syndrome, caused by micronutrient deficiencies. Muscle Nerve 57: 33-39, 2018.

Electrophysiologic features of SYT2 mutations causing a treatable neuromuscular syndrome

OBJECTIVES

To describe the clinical and electrophysiologic features of synaptotagmin II (SYT2) mutations, a novel neuromuscular syndrome characterized by foot deformities and fatigable ocular and lower limb weakness, and the response to modulators of acetylcholine release.

METHODS

We performed detailed clinical and neurophysiologic assessment in 2 multigenerational families with dominant SYT2 mutations (c.920T>G [p.Asp307Ala] and c.923G>A [p.Pro308Leu]). Serial clinical and electrophysiologic assessments were performed in members of one family treated first with pyridostigmine and then with 3,4-diaminopyridine.

RESULTS

Electrophysiologic testing revealed features indicative of a presynaptic deficit in neurotransmitter release with posttetanic potentiation lasting up to 60 minutes. Treatment with 3,4-diaminopyridine produced both a clinical benefit and an improvement in neuromuscular transmission.

CONCLUSION

SYT2 mutations cause a novel and potentially treatable complex presynaptic congenital myasthenic syndrome characterized by motor neuropathy causing lower limb wasting and foot deformities, with reflex potentiation following exercise and a uniquely prolonged period of posttetanic potentiation.

Infectious neuropathies

PURPOSE OF REVIEW

Infections are important, potentially treatable causes of peripheral nervous system disease. This article reviews the clinical presentation and management of several common peripheral nervous system diseases due to viral, bacterial, spirochetal, and parasitic infections.

RECENT FINDINGS

The clinical presentation and evaluation of infectious peripheral nervous system diseases are well established. Advances in the treatment and, in some cases, the prevention of these diseases are still evolving.

SUMMARY

A diverse range of peripheral nervous system diseases, including peripheral neuropathy, radiculopathy, radiculomyelopathy, cranial neuropathy, and motor neuropathy, are caused by numerous infectious agents. In some patients, peripheral neuropathy may be a side effect of anti-infectious drugs. Infectious neuropathies are important to recognize as they are potentially treatable. This article discusses the clinical presentation, evaluation, and treatment of several common peripheral nervous system diseases caused by viral, bacterial, spirochetal, and parasitic infections, as well as some peripheral nerve disorders caused by adverse effects of the treatments of these infectious diseases.

Visualization of the diaphragm muscle with ultrasound improves diagnostic accuracy of phrenic nerve conduction studies

INTRODUCTION

Evaluation of phrenic neuropathy (PN) with phrenic nerve conduction studies (PNCS) is associated with false negatives. Visualization of diaphragmatic muscle twitch with diaphragm ultrasound (DUS) when performing PNCS may help to solve this problem.

METHODS

We performed bilateral, simultaneous DUS-PNCS in 10 healthy adults and 12 patients with PN. The amplitude of the diaphragm compound muscle action potential (CMAP) (on PNCS) and twitch (on DUS) was calculated.

RESULTS

Control subjects had <38% side-to-side asymmetry in twitch amplitude (on DUS) and 53% asymmetry in phrenic CMAP (on PCNS). In the 12 patients with PN, 12 phrenic neuropathies were detected. Three of these patients had either significant side-to-side asymmetry or absolute reduction in diaphragm movement that was not detected with PNCS. There were no cases in which the PNCS showed an abnormality but the DUS did not.

CONCLUSIONS

The addition of DUS to PNCS enhances diagnostic accuracy in PN.

The diagnosis and treatment of myotonic disorders

Myotonia is a defining clinical symptom and sign common to a relatively small group of muscle diseases, including the myotonic dystrophies and the nondystrophic myotonic disorders. Myotonia can be observed on clinical examination, as can its electrical correlate, myotonic discharges, on electrodiagnostic testing. Research interest in the myotonic disorders continues to expand rapidly, which justifies a review of the scientific bases, clinical manifestations, and numerous therapeutic approaches associated with these disorders. We review the pathomechanisms of myotonia, the clinical features of the dystrophic and nondystrophic myotonic disorders, and the diagnostic approach and treatment options for patients with symptomatic myotonia.

Electrodiagnosis of myotonic disorders

Clinical and electrical myotonia is caused by a small group of neuromuscular disorders. This article reviews myotonia and its differential diagnosis. The use of electrodiagnostic testing to evaluate the primary myotonic disorders (myotonic dystrophy and the nondystrophic myotonias) is also discussed.

Unexpected neuroimaging abnormalities in patients with apparent C8 radiculopathy: broadening the clinical spectrum

INTRODUCTION

C8-root impingement by C7/T1 lesions on neuroimaging studies is not consistently observed in C8 radiculopathy. We hypothesized that C7 or T1 root lesions (with a pre- or postfixed plexus) or cervical myelopathy might explain some "C8 radiculopathies" without C8 root compression.

METHODS

Retrospective analysis of cervical neuroimaging in 31 consecutive patients with EMG-confirmed C8 radiculopathy.

RESULTS

Five patients (16%) had C8-root compression at C7/T1. Of those without C8-root compression, 5 (16%) had C7-root compression at C6/7, one (3%) had T1-root compression at T1/T2, 7 (23%) had cervical cord compression at or above the C6/7 level, 4 (13%) had intramedullary cervical lesions, and 9 (29%) had mild or nonspecific findings.

CONCLUSIONS

C8 radiculopathy without C8-root compression may be due to C7-root compression in the setting of a "prefixed" brachial plexus, upper cervical cord compression with vascular compromise of the distal cervical spinal cord ("myelopathic hand"), or intramedullary cervical cord lesions.

Open-label trial of recombinant human insulin-like growth factor 1/recombinant human insulin-like growth factor binding protein 3 in myotonic dystrophy type 1

OBJECTIVE

To evaluate the safety and tolerability of recombinant human insulin-like growth factor 1 (rhIGF-1) complexed with IGF binding protein 3 (rhIGF-1/rhIGFBP-3) in patients with myotonic dystrophy type 1 (DM1).

DESIGN

Open-label dose-escalation clinical trial.

SETTING

University medical center.

PARTICIPANTS

Fifteen moderately affected ambulatory participants with genetically proven myotonic dystrophy type 1.

INTERVENTION

Participants received escalating dosages of subcutaneous rhIGF-1/rhIGFBP-3 for 24 weeks followed by a 16-week washout period.

MAIN OUTCOME MEASURES

Serial assessments of safety, muscle mass, muscle function, and metabolic state were performed. The primary outcome variable was the ability of participants to complete 24 weeks receiving rhIGF-1/ rhIGFBP-3 treatment.

RESULTS

All participants tolerated rhIGF-1/rhIGFBP-3. There were no significant changes in muscle strength or functional outcomes measures. Lean body muscle mass measured by dual-energy x-ray absorptiometry increased by 1.95 kg (P < .001) after treatment. Participants also experienced a mean reduction in triglyceride levels of 47 mg/dL (P = .002), a mean increase in HDL levels of 5.0 mg/dL (P = .03), a mean reduction in hemoglobin A(1c) levels of 0.15% (P = .03), and a mean increase in testosterone level (in men) of 203 ng/dL (P = .002) while taking rhIGF-1/rhIGFBP-3. Mild reactions at the injection site occurred (9 participants), as did mild transient hypoglycemia (3), lightheadedness (2), and transient papilledema (1).

CONCLUSIONS

Treatment with rhIGF-1/rhIGFBP-3 was generally well tolerated in patients with myotonic dystrophy type 1. Treatment with rhIGF-1/rhIGFBP-3 was associated with increased lean body mass and improvement in metabolism but not increased muscle strength or function. Larger randomized controlled trials would be needed to further evaluate the efficacy and safety of this medication in patients with neuromuscular disease.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00233519.

Mexiletine is an effective antimyotonia treatment in myotonic dystrophy type 1

OBJECTIVE

To determine if mexiletine is safe and effective in reducing myotonia in myotonic dystrophy type 1 (DM1).

BACKGROUND

Myotonia is an early, prominent symptom in DM1 and contributes to decreased dexterity, gait instability, difficulty with speech/swallowing, and muscle pain. A few preliminary trials have suggested that the antiarrhythmic drug mexiletine is useful, symptomatic treatment for nondystrophic myotonic disorders and DM1.

METHODS

We performed 2 randomized, double-blind, placebo-controlled crossover trials, each involving 20 ambulatory DM1 participants with grip or percussion myotonia on examination. The initial trial compared 150 mg of mexiletine 3 times daily to placebo, and the second trial compared 200 mg of mexiletine 3 times daily to placebo. Treatment periods were 7 weeks in duration separated by a 4- to 8-week washout period. The primary measure of myotonia was time for isometric grip force to relax from 90% to 5% of peak force after a 3-second maximum grip contraction. EKG measurements and adverse events were monitored in both trials.

RESULTS

There was a significant reduction in grip relaxation time with both 150 and 200 mg dosages of mexiletine. Treatment with mexiletine at either dosage was not associated with any serious adverse events, or with prolongation of the PR or QTc intervals or of QRS duration. Mild adverse events were observed with both placebo and mexiletine treatment.

CONCLUSIONS

Mexiletine at dosages of 150 and 200 mg 3 times daily is effective, safe, and well-tolerated over 7 weeks as an antimyotonia treatment in DM1.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that mexiletine at dosages of 150 and 200 mg 3 times daily over 7 weeks is well-tolerated and effective in reducing handgrip relaxation time in DM1.

Evoked myotonia can be "dialed-up" by increasing stimulus train length in myotonic dystrophy type 1

It is unknown how evoked myotonia varies with stimulus frequency or train length, or how it compares to voluntary myotonia in myotonic dystrophy type 1 (DM1). First dorsal interosseous (FDI) tetanic contractions evoked by trains of 10-20 ulnar nerve stimuli at 10-50 HZ were recorded in 10 DM1 patients and 10 normals. For comparison, maximum voluntary handgrip contractions were also recorded. An automated computer program placed cursors along the declining (relaxation) phase of the force recordings at 90% and 5% of peak force (PF) and calculated relaxation times (RTs) between these points. For all stimulus frequencies and train lengths, evoked RTs were much shorter, and evoked PFs were much greater in normals than in DM1. In normals, evoked RT was independent of stimulus frequency and train length, while in DM1 RT was longer for train lengths of 20 stimuli (mean: 9 s in DM1; 0.20 in normals) than for 10 stimuli (mean: 3 s in DM1, 0.19 in normals), but it did not change with stimulus frequency. In both groups PF increased greatly as stimulus frequency rose from 10-50 HZ but only slightly as train length rose from 10-20 stimuli. Voluntary handgrip RT (mean: 1.9 s) was less than evoked FDI RT (mean: 9 s). In DM1, evoked RT can be "dialed up" by increasing stimulus train length. Evoked myotonia testing utilizing a stimulus paradigm of at least 20 stimuli at 30-50 HZ may be useful in antimyotonic drug trials, particularly when grip RT is normal or equivocal.

Late-onset Tay-Sachs disease: the spectrum of peripheral neuropathy in 30 affected patients

Late-onset Tay-Sachs (LOTS) disease is a chronic, progressive, lysosomal storage disorder caused by a partial deficiency of beta-hexosaminidase A (HEXA) activity. Deficient levels of HEXA result in the intracellular accumulation of GM2-ganglioside, resulting in toxicity to nerve cells. Clinical manifestations primarily involve the central nervous system (CNS) and lower motor neurons, and include ataxia, weakness, spasticity, dysarthria, dysphagia, dystonia, seizures, psychosis, mania, depression, and cognitive decline. The prevalence of peripheral nervous system (PNS) involvement in LOTS has not been well documented, but it has traditionally been thought to be very low. We examined a cohort of 30 patients with LOTS who underwent clinical and electrophysiologic examination, and found evidence of a predominantly axon loss polyneuropathy affecting distal nerve segments in the lower and upper extremities in eight patients (27%).

Computerized hand grip myometry reliably measures myotonia and muscle strength in myotonic dystrophy (DM1)

The aim of this study was to develop a reliable, sensitive, quantitative measure of grip myotonia and strength and to determine whether CTG repeat length is correlated with grip myotonia and with muscle strength in myotonic dystrophy type 1 (DM1). Three maximum voluntary isometric contractions (MVICs) of the finger flexors (i.e., handgrip) were recorded on 2 successive days using a computerized handgrip myometer in 29 genetically confirmed DM1 patients and 17 normals. An automated computer program calculated MVIC peak force (PF) and relaxation times (RTs) along the declining (relaxation) phase of the force recordings at 90%, 75%, 50%, 10%, and 5% of PF. Patients also underwent quantitative strength testing (QST) manual muscle testing (MMT). The patients had longer grip RTs and lower PFs than normals. RT (90% to 5%) was above the normal mean +2.5 SD in 25 (86%) patients. In DM1, prolongation of RT was mainly in the terminal (50% to 5%), rather than the initial (90% to 50%) phase of relaxation. PFs and RTs for each patient were reproducible on consecutive days. RTs were positively correlated with leukocyte CTG repeat length, whereas measures of muscle strength, such as PF, QST, and MMT, were negatively correlated with repeat length. We conclude that computerized handgrip myometry provides a sensitive, reliable measure of myotonia and strength in DM1 and offers a method to assess natural history and response to treatment.

Severity, type, and distribution of myotonic discharges are different in type 1 and type 2 myotonic dystrophy

To characterize and compare electrical myotonia in myotonic dystrophy type 1 (DM1) and type 2 (DM2), 16 patients with genetically confirmed DM1 and 17 patients with DM2 underwent standardized concentric needle electromyography of deltoid, biceps, extensor digitorum communis, first dorsal interosseous, tensor fascia lata (TFL), vastus lateralis (VL), tibialis anterior, and thoracic paraspinal muscles. Eight needle insertions per muscle were made by electromyographers blinded to DM type who recorded the presence and type of myotonia (e.g., classic waxing-waning or less specific waning discharges). Manual muscle testing was performed by a physical therapist. Overall, myotonia was more elicitable in DM1 than DM2; only in VL and TFL was myotonia more elicitable in DM2 than DM1. The major type of myotonia was waxing-waning in DM1, and waning in DM2. Four DM2 (24%), but no DM1 patients had only waning myotonia. In the arms, myotonia was distally predominant in both DM1 and DM2. In the legs, it was distally predominant in DM1, but both proximal and distal in DM2. The severity of myotonia was positively correlated with muscle weakness and with the presence of waxing and waning discharges in DM1, but with neither in DM2. Thus, myotonia is qualitatively and quantitatively different in DM1 than DM2. Except for proximal leg muscles, myotonia is more evocable in DM1 than DM2. It tends to be waxing-waning in DM1 but waning in DM2, thus making electrodiagnosis of DM2 more challenging. Its severity correlates with muscle weakness and the presence of waxing-waning discharges in DM1 but not DM2.

Clinical evaluation of membrane excitability in muscle channel disorders: potential applications in clinical trials

Muscle channelopathies are inherited disorders that cause paralysis and myotonia. Molecular technology has contributed immeasurably to diagnostic testing, to correlation of genotype with phenotype, and to insight into the pathophysiology of these disorders. In most cases, the diagnosis of muscle channelopathy is still made on clinical grounds, but is supported by ancillary laboratory and electrodiagnostic testing such as serum potassium measurement, exercise testing, repetitive nerve stimulation, needle electromyography, calculation of muscle fiber conduction velocity, or electromyography power spectra. Although provocative glucose or potassium challenges are now infrequently performed, they have contributed greatly to our understanding of the pathophysiology of these disorders, and to our ability to differentiate between periodic paralysis types. Despite considerable progress, ample opportunity remains for future clinical research, particularly in expanding genotype-phenotype correlations and in optimizing electrodiagnostic methods. With respect to diagnostic testing, there is a need for accurate, efficient, and cost-effective bedside testing, given the substantial proportion (as high as 20%) of genetically undefined cases. Even in genetically defined cases, minimal clinical expressivity due to incomplete penetrance poses a significant challenge to currently available nonmolecular testing.

Dispersion of compound muscle action potential in hereditary neuropathies and chronic inflammatory demyelinating polyneuropathy

Distal compound muscle action potential (DCMAP) dispersion, defined as a DCMAP duration > or = 9 ms, and proximal-distal (P-D) CMAP dispersion are considered useful in the electrodiagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP). Distal and P-D CMAP dispersion have not been fully studied in hereditary neuropathies, and it is not known whether these measures distinguish hereditary from acquired demyelination. We compared DCMAP duration and P-D CMAP dispersion in 91 genetically characterized hereditary neuropathies and 33 subjects with CIDP. DCMAP dispersion was more frequent in nerves affected by CIDP (41.5%) than in Charcot-Marie-Tooth disease (CMT)1A (24.4%), CMT1B (7.4%), hereditary neuropathy with liability to pressure palsies (HNPP) (10.5%), or CMTX (9.8%). P-D CMAP dispersion was more frequent in CIDP (27.7% of nerves) than in hereditary neuropathies (16.3%) when applying American Academy of Neurology (AAN) criteria; however, its frequency was similar in CIDP and the hereditary neuropathies using the more restrictive criteria of the American Association of Neuromuscular and Electrodiagnostic Medicine (AANEM). Although dispersion is more common in CIDP than in the hereditary neuropathies, DCMAP and P-D dispersion occur in at least one motor nerve in a significant proportion of hereditary neuropathies, and cannot be used in isolation to distinguish acquired from hereditary demyelination.

Acute inflammatory demyelinating polyneuropathy: Contribution of a dispersed distal compound muscle action potential to electrodiagnosis

Prolonged duration of the distal compound muscle action potential (DCMAP) ("DCMAP dispersion") is useful in the electrodiagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP) with good specificity in distinguishing CIDP from amyotrophic lateral sclerosis (ALS) and diabetic polyneuropathy, but its role in the electrodiagnosis of acute inflammatory demyelinating polyneuropathy (AIDP) is unclear. This study addresses this issue by determining the optimal cutoff for DCMAP duration using receiver operating characteristic (ROC) analysis in 207 motor nerves from 53 clinically defined AIDP patients compared to 148 motor nerves from 55 ALS patients. We also determined whether the presence of DCMAP dispersion improves the sensitivity of four of the most sensitive published sets of electrodiagnostic criteria for AIDP. Using the ROC-derived optimal DCMAP duration cutoff of 8.5 ms, DCMAP dispersion was found in at least one motor nerve in 66% of subjects with AIDP compared to 9% of subjects with ALS. DCMAP dispersion improved the sensitivity of the four tested criteria sets to 76%-87% from 43%-77%. Moreover, of 13 AIDP patients who met none of the four published criteria sets, 5 (38%) had at least one dispersed DCMAP. These findings indicate that the presence of DCMAP dispersion adds electrodiagnostic sensitivity to the currently published criteria sets, while maintaining reasonably high specificity against a prototypical disorder of the primary motor neuron with axon loss.

Painful small-fiber neuropathy in Sjogren syndrome

Of 20 consecutive patients with Sjögren neuropathy, 16 (80%) presented with burning feet and 12 (60%) with non-length-dependent sensory symptoms. Leg and thigh skin biopsies, performed in 13 patients, including 7 with normal electrophysiology, showed either reduced epidermal nerve fiber (ENF) density or abnormal morphology. ENF loss was frequently non length dependent, suggesting that patients with this disorder commonly have a small-fiber sensory neuronopathy rather than a "dying-back" axonopathy.

Genotype-phenotype correlation in a family with late onset CMT and an MPZ lys236del mutation

An in frame, lys236 deletion in the intracytoplasmic domain of myelin protein zero (MPZ) has recently been designated as a mutation possibly associated with Charcot-Marie-Tooth disease (CMT) but requiring further documentation. In this report we present a detailed clinical, electrophysiological, and genotype correlation in three generations of a family with the MPZ lys236del mutation and provide further evidence that this mutation is associated with CMT. The MPZ lys236del mutation is associated with an autosomal dominant, adult onset CMT phenotype, with variable penetrance ranging from an asymptomatic state to foot deformities, pedal numbness, and muscle cramps. Nerve conduction studies disclose intermediate range, somewhat non-uniform slowing of motor nerve conduction, which is accentuated in forelimb rather than distal nerve segments. Based on the contrasting finding of entirely normal conduction velocities (CV) in a genetically affected 15 year old in this family, it remains to be established whether CV slowing with this mutation is progressive in life, a pattern that would contrast with CMT1a (PMP22 gene duplication).

Quantitative analysis of the “warm-up” phenomenon in myotonic dystrophy type 1

To quantitate improvement in hand-grip myotonia and muscle strength (i.e., the "warm-up" phenomenon) in myotonic dystrophy type 1 (DM1), six successive, standardized maximum voluntary isometric contractions (MVICs) were recorded on 2 separate days using a computerized isometric hand-grip myometer in 25 genetically confirmed DM1 patients and in 17 normal controls. An automated computer program placed cursors along the declining (relaxation) phase of the MVICs at 90%, 50%, and 5% of peak force (PF) and calculated relaxation times (RTs) between these points. Mean 90% to 5% RT (a measure of myotonia) rapidly declined from 2.5 s in MVIC 1 to 0.8 s in MVIC 6 (warm-up = 1.7 s) in DM1; in controls, it remained 0.4 s for all six MVICs (warm-up = 0). In DM1, 70% of warm-up occurred between MVIC 1 and 2, almost exclusively in the terminal 50% to 5% phase of muscle relaxation. Day 1 warm-up was highly correlated with the severity of myotonia, and with day 2 warm-up. Improvement in myotonia was not accompanied by either transient paresis or improvement in PF. We conclude that, with this testing paradigm: warm-up of myotonia in DM1 can be reliably measured; is proportional to severity of myotonia; occurs rapidly, being most prominent between the first and second grips; mainly results from shortening of the terminal phase of muscle relaxation; and is not accompanied by significant warm-up in force output.

Plantar nerve AP and skin biopsy in sensory neuropathies with normal routine conduction studies

OBJECTIVE

To assess the medial plantar nerve action potential (NAP) and skin biopsy in the evaluation of suspected distal sensory neuropathies (SN) with normal routine nerve conduction studies (NCS).

METHODS

A total of 110 consecutive patients with suspected distal SN and normal routine NCS underwent medial plantar NAP testing and punch skin biopsy. Patients were clinically stratified as having pure small fiber sensory neuropathy (SFSN), or distal SN with large fiber involvement (SN-LFI).

RESULTS

A total of 56 patients were classified as SN-LFI and 54 SFSN. The medial plantar NAP, a measure of large fiber function, was abnormal in 31.8% of patients, more frequently in SN-LFI than SFSN. Distal leg epidermal nerve fiber (ENF) density, a measure of small fibers, was reduced in 47.3% of biopsies, with isolated ENF morphologic changes in 29.1% and normal findings in 23.6%. Biopsy abnormalities were more severe and prevalent in SN-LFI than in SFSN. In patients with a normal medial plantar NAP, distal leg biopsy showed reduced ENF density in 34.7%, and isolated morphologic changes in a further 37% of cases.

CONCLUSIONS

The medial plantar nerve action potential and skin biopsy are complementary in evaluation of distal SN with normal routine NCS. Small sensory nerve fibers are affected early in SN, and more severely so when large fiber involvement is apparent clinically.

Leukocyte CTG repeat length correlates with severity of myotonia in myotonic dystrophy type 1

OBJECTIVE

To quantitate hand muscle myotonia and to assess the relationship between CTG repeat length and myotonia in myotonic dystrophy type 1 (DM1).

METHODS

First dorsal interosseous twitch and tetanic contractions evoked by single and 10-Hz ulnar nerve stimulation were recorded with a force transducer in 15 patients with genetically confirmed DM1 and 15 control subjects. An automated computer program analyzed three single and three tetanic recordings per subject on 2 successive days by placing cursors along the declining (relaxation) phase of the force recordings at 90, 50, and 5% of peak force (PF) and calculating relaxation times (RT) between these points.

RESULTS

Tetanic and twitch RT was longer and PF lower in patients than subjects. RT (90 to 5%) was above the normal mean + 2.5 SD in 13 tetanic (87%) and 11 (73%) twitch patient recordings. In DM1, prolongation of RT was due mainly to delay in the terminal (50 to 5%), rather than the initial (90 to 50%) phase of relaxation, and was much greater in tetanic than single-twitch recordings. Mean test-retest variability was 19% for tetanic RT and 16% for tetanic PF. In DM1, both tetanic and twitch RT were positively correlated with leukocyte CTG repeat length.

CONCLUSIONS

In DM1, myotonia of intrinsic hand muscles can be quantitated reliably by automated analysis of tetanic and twitch RT, targeting, in particular, the terminal phase of muscle relaxation after tetanic stimulation. Severity of hand muscle myotonia depends on CTG repeat length consistent with a "triplet repeat dosage" effect on chloride channel mRNA splicing and function.

Evaluation of patients with recurrent symptoms after ulnar nerve transposition

Focal entrapment of the ulnar nerve occurs most frequently in the region of the elbow, at the ulnar groove or beneath the humeroulnar aponeurosis. Surgical treatment commonly involves transposition of the nerve anterior to the medial epicondyle, in the antecubital fossa. Symptoms may recur after surgery, and, to assess their etiology, we studied 10 patients with recurrent ulnar symptoms after transposition. Conventional motor and sensory conduction studies were performed, as was mapping of nerve position using submaximal stimuli. In 9 of 10 patients, the ulnar nerve at the elbow was located adjacent to the medial epicondyle, rather than in the antecubital fossa. Focal slowing in the region of the elbow was noted in 8 patients, and an additional site of focal slowing was found in the forearm in 3 patients. We conclude that in patients with recurrent symptoms after ulnar nerve transposition postoperative position of the ulnar nerve may be medial, often near the medial epicondyle. This location may predispose the nerve to recurrent trauma or cause traction on the nerve at more distal locations within the forearm. The prevalence of this medial location of the ulnar nerve in asymptomatic postsurgical patients is unknown.

Dispersion of the distal compound muscle action potential in chronic inflammatory demyelinating polyneuropathy and carpal tunnel syndrome

Median neuropathy at the wrist can confound the electrodiagnosis of chronic inflammatory demyelinating polyneuropathy (CIDP), since both conditions can prolong median distal motor latency. Dispersion of the distal CMAP (DCMAP) has recently emerged as a potentially useful adjunct in the electrodiagnosis of CIDP, with good specificity in distinguishing CIDP from certain axon-loss disorders. However, it is uncertain whether focal compression neuropathies produce dispersion of the DCMAP in a manner similar to CIDP. In this study we compared median DCMAP duration in 27 patients with CIDP and 86 with carpal tunnel syndrome, using 39 patients with non-neuropathic musculoskeletal pain syndromes as electrophysiologic controls. We found that, in contrast to CIDP, dispersion of the median DCMAP is uncommon, even in advanced carpal tunnel syndrome, being seen in only 8 of 103 (7.8%) hands. Although the pathophysiologic reasons for a differential effect of focal compression-mediated demyelination and multifocal immune-mediated demyelination (CIDP) on DCMAP duration are uncertain, our findings suggest that the presence of dispersion of the median DCMAP may prove useful in distinguishing immune-mediated demyelination from compression neuropathy alone.

A Bayesian argument against rigid cut-offs in electrodiagnosis of median neuropathy at the wrist

BACKGROUND

Nerve conduction (NC) tests, using rigid cut-offs separating normal from abnormal test values, are commonly used to confirm median neuropathy at the wrist (MNW). The authors studied patients with clinically defined mild MNW and a normal median distal motor latency to determine 1) how much sensory or mixed NC test results increase (or decrease) the probability of MNW and 2) the NC test values required to confirm (or exclude) MNW for the range of pretest probabilities of MNW.

METHODS

Palmar, digit 4 (D4), and digit 2 (D2) median NC tests were reviewed in 125 hands with mild carpal tunnel syndrome (CTS) and 100 control hands with musculoskeletal pain. Receiver operating characteristic curves and interval likelihood ratios were plotted for the three tests. Using Bayes theorem, post-test probability of MNW was then determined for the range of pretest probabilities and NC test values.

RESULTS

Receiver operating characteristic curves showed that for a set specificity of 97%, palmar and D4 studies had higher electrodiagnostic utility than D2 studies with cut-off test values (sensitivities of 0.3 msec, 64.0%; 0.4 msec, 71.2%; and 50 m/sec, 44.8%). However, Bayesian analysis showed that to confirm MNW more conservative cut-off values (palmar 0.5 msec, D4 0.7 msec, D2 44 m/sec) were required for pretest probabilities <or=50%, whereas borderline abnormal values (palmar 0.4 msec, D4 0.5 msec, D2 48 m/sec) sufficed when pretest probabilities were >or=75%. Conversely, normal test values could exclude MNW only for pretest probabilities <25%.

CONCLUSIONS

For a given NC test value, post-test probability of MNW can be determined from the estimated pretest probability (derived from clinical data), interval likelihood ratios, and Bayes theorem. Use of rigid cut-off values to confirm MNW is problematic, because more conservative cut-offs are required for low pretest probability. Conversely, NC tests with sensitivity <95% cannot exclude MNW when pretest probability is high.

Dispersion of the distal compound muscle action potential as a diagnostic criterion for chronic inflammatory demyelinating polyneuropathy

OBJECTIVE

To assess distal compound muscle action potential (DCMAP) duration as a diagnostic criterion for chronic inflammatory demyelinating polyneuropathy (CIDP).

BACKGROUND

Current electrodiagnostic criteria for CIDP have high specificity but limited sensitivity. Prolonged DCMAP duration has been reported in acute inflammatory demyelinating polyneuropathy. The authors have compared DCMAP duration in patients with CIDP, diabetic polyneuropathy (DP), ALS, and musculoskeletal pain syndrome (MSP) to determine whether it enhances the sensitivity of electrodiagnostic criteria for CIDP.

METHODS

Data from 23 CIDP, 34 DP, 34 ALS, and 54 MSP patients were reviewed. The time interval between onset of the first negative peak and return to baseline of the last negative peak of the DCMAP was calculated for each nerve. To distinguish CIDP from DP, ALS, and MSP, optimal cutoff values for DCMAP duration were achieved with receiver-operating characteristic curves. The sensitivity and specificity of these cutoff values were compared with each of four sets of electrodiagnostic criteria for CIDP.

RESULTS

Mean DCMAP duration in CIDP was significantly longer than in DP, ALS, and MSP. The sensitivity of existing electrodiagnostic criteria for CIDP ranged between 0.43 and 0.61. Their specificity vs DP or ALS was 0.91 to 1. Using DCMAP duration of >/=9 milliseconds for any of four motor nerves yielded a sensitivity of 0.78 for CIDP and specificity of 0.94 vs DP or ALS. Adding DCMAP duration criteria to any one of the three accepted criteria enhanced their sensitivity with little sacrifice of specificity.

CONCLUSION

Quantitation of DCMAP dispersion shows promise as a sensitive and specific adjunctive electrodiagnostic criterion for CIDP.

Electrodiagnosis of ulnar neuropathy at the wrist: conduction block versus traditional tests

BACKGROUND

Compared to ulnar neuropathy at the elbow (UNE), ulnar neuropathy at the wrist (UNW) is rarer and more difficult to localize with routine electrophysiologic studies.

METHODS

By stimulating the ulnar nerve at the wrist and palm, and recording from first dorsal interosseous (FDI), the sensitivity and specificity of conduction block (CB) and slow conduction velocity (CV) of FDI fibers across the wrist was compared to traditional electrodiagnostic techniques for localization of UNW. Twenty patients with clinically defined UNW (due mainly to wrist trauma), 30 normal controls, and 20 disease controls with severe (n = 10) and mild (n = 10) UNE were evaluated prospectively. The upper (mean +2.5 SD) and lower (mean -2.5 SD) limits for all measurements were derived from the normal controls.

RESULTS

The UNW patients showed: slow wrist-palm FDI CV (<37 m/s) in 16 (80%); definite or probable CB in 14 (70%); prolonged distal latency (DL) to FDI (>4.5 milliseconds) in 12 (60%), to ulnar-innervated palmar interosseous (PI) versus median-innervated lumbrical (L) in 12 (60%), and to abductor digiti minimi (ADM) in 11 (55%). However, only CB and slow wrist-palm FDI CV (<37 m/s) were specific for UNW; prolonged DL to FDI was found in 4 patients (40%), to ADM in 4 patients (40%), and to PI in 1 patient (10%) with severe UNE. Overall, CB or slow wrist-palm FDI CV was present in 19 patients with UNW (95%). EMG failed to differentiate UNW from UNE, because forearm ulnar-innervated muscles were typically normal in UNW, but also often normal in mild UNE.

CONCLUSIONS

In UNW, an additional palmar stimulation site improves electrodiagnostic yield, and demonstrates that CB is an important cause of muscle weakness.

Class of nerve fiber involvement in sensory neuropathies: clinical characterization and utility of the plantar nerve action potential

Precise classification of distal sensory polyneuropathies (SN) according to fiber type involvement is desirable for clinical and research purposes. The sural sensory response has served as an electrophysiologic gold standard for the assessment of large-fiber sensory dysfunction. However, patients labeled as having small-fiber sensory neuropathies on the basis of a normal sural response frequently have clinical evidence of large-fiber dysfunction. The surface-recorded medial plantar potential has shown promise as a more sensitive indicator of large-fiber sensory dysfunction, but is not widely accepted because of concerns about age effects and a lack of large well-controlled studies in SN. We have thus correlated clinical type of SN: large-fiber sensory neuropathies (LFSN), small-fiber sensory neuropathies (SFSN), and mixed (large- and small-fiber) sensory neuropathies (MFSN) with sural and medial plantar nerve conduction studies in 133 consecutive patients with distal SN and 108 control subjects. A combination of stringent clinical characterization and electrophysiologic features, especially the surface-recorded medial plantar rather than sural potential, was complementary, and permitted a more clear separation of LFSN, MFSN, and SFSN than with either approach used alone.

Conduction slowing in diabetic distal polyneuropathy

The pathophysiologic significance of motor conduction slowing observed in diabetic distal symmetrical polyneuropathy (DSP) remains controversial. We have used multiple linear regression analysis of compound muscle action potential (CMAP) amplitude vs. motor conduction velocity (CV) and distal latency (DL) in 57 patients with diabetic DSP and 34 patients with amyotrophic lateral sclerosis (ALS) to determine whether motor conduction slowing in diabetic DSP is due mainly to loss of large axons as in ALS or whether there is an additional demyelinative component. We found amplitude-dependent slowing of CV and DL in both diabetic DSP and ALS in the upper and lower extremities, consistent with a loss of large myelinated fibers. However, in diabetic DSP, there was also significant amplitude-independent slowing in intermediate but not distal nerve segments, supportive of an additional demyelinative component. CMAP amplitude vs. CV and DL regression analyses using ALS as a control group for relatively pure axon loss may provide pathophysiologic information about motor nerves in other neuropathic disorders.

Evidence in support of a feedback-sensitive central timekeeper for an over-learned repetitive motor behavior (pencil shading)

PURPOSE

To demonstrate the presence of a CNS timekeeper for an over-learned repetitive voluntary movement (pencil shading), and to learn if the timekeeper is influenced by changes in sensory feedback.

METHODS

Self-paced pencil shading; fast, maximally-fast, and slow hand waving, as well as enhanced physiologic tremor (EPT) were recorded on 3 separate occasions with a surface-mounted accelerometer placed on the hand in 9 normal volunteers. Variation in inter-trial peak frequency was calculated. Shading and EPT were also recorded with and without visual masking in 9 normals and in 2 deafferented patients. Variation in intra-trial beat-to-beat intervals, a measure of movement regularity, was calculated.

RESULTS

Shading and maximally-fast waving displayed preferred frequencies with no more variability in peak frequency between trials than did EPT, while slow and fast waving had significant inter-trial variability. Variation in beat-to-beat intervals for the shading task was less in controls than for EPT, and less in controls than for the patients in both the masked and unmasked conditions. In addition, in the masked condition, pencil shading by the patients was performed with much higher amplitude and lower frequency than by the controls.

CONCLUSIONS

These data support the hypothesis that certain repetitive voluntary movements, such as pencil shading, are paced by central timekeepers that are influenced by changes in sensory feedback.

Electrodiagnostic approach to the patient with suspected mononeuropathy of the upper extremity

Upper extremity mononeuropathies are common. Most are due to compression, whereas others occur in the setting of systemic disorders (e.g., diabetes) or with coexistent polyneuropathies. Electrophysiologic studies are essential in most cases, and provide critical information regarding localization, severity, activity, chronicity, and underlying pathophysiological mechanisms. Insights gleaned from the electrodiagnostic report guide clinicians in the optimal management of mononeuropathies of the upper extremity.

Gentle dorsal root retraction and dissection can cause areflexia: implications for intraoperative monitoring during "selective" partial dorsal rhizotomy

During partial dorsal rhizotomy (PDR), intraoperative dorsal rootlet stimulation often evokes nonreflex, rather than reflex, motor responses that are due to costimulation of adjacent ventral roots. Intraoperative areflexia typically predicts that motor responses evoked by dorsal rootlet stimulation are nonreflexive. The cause of areflexia during PDR is in part due to anesthesia, but other mechanisms are likely to play a role as well. In this study of three consecutive patients undergoing lumbosacral neurosurgery, soleus H-reflexes evoked by tibial nerve stimulation at the popliteal fossa were found to suddenly decline in amplitude following retraction and gentle dissection of the S-1 dorsal root. In one areflexic patient, dorsal rootlet stimulation proximal to the main site of dissection evoked soleus H-reflexes, although they could not be evoked by tibial nerve stimulation. We conclude that the gentle retraction and dissection of dorsal rootlets that occurs during PDR can induce conduction block of reflex afferents. High-intensity dorsal rootlet stimulation distal to the site of conduction block may then evoke not reflex responses, but rather nonreflex motor responses, due to the costimulation of adjacent ventral roots.

Distal myasthenia gravis with a decrement, an increment, and denervation

We present two patients with distal myasthenia gravis poorly responsive to immunomodulatory therapy. In addition to a typical decrement on slow repetitive nerve stimulation, both had borderline to low compound muscle action potential (CMAP) amplitudes, a large increment in CMAP amplitude and area after exercise, and active denervation in distal muscles. Both had elevated acetylcholine receptor antibody (AChR Ab) levels, but normal voltage-gated calcium channel antibody levels. We hypothesize that these electrophysiological findings represent a more severe form of myasthenia gravis.

Localization of ulnar neuropathy with conduction block across the elbow

We performed short segment incremental stimulation on 13 consecutive patients with ulnar neuropathy across the elbow (UNE) and conduction block. Conduction block occurred proximal to the medial epicondyle in 62%, at the epicondyle in 23%, and below the elbow in 15%. The ulnar nerve may be more prone to external compression above the elbow than previously recognized. Short segment incremental studies are useful to identify conduction block above the elbow in such patients.

Musculoskeletal and neurologic outcomes in patients with previously treated Lyme disease

BACKGROUND

Previous follow-up studies of patients with Lyme disease suggest that disseminated infection may be associated with long-term neurologic and musculoskeletal morbidity.

OBJECTIVE

To determine clinical and functional outcomes in persons who were treated for Lyme disease in the late 1980s.

DESIGN

Population-based, retrospective cohort study.

SETTING

Nantucket Island, Massachusetts.

PARTICIPANTS

186 persons who had a history of Lyme disease (case-patients) and 167 persons who did not (controls).

MEASUREMENTS

Standardized medical history, physical examination, functional status measure (Medical Outcomes Study 36-item Short Form Health Survey [SF-36]), mood state assessment (Profile of Mood States), neurocognitive tests, and serologic examination.

RESULTS

The prevalence of Lyme disease among adults on Nantucket Island was estimated to be 14.3% (95% CI, 9.3% to 19.1%). In multivariate analyses, persons with previous Lyme disease (mean time from infection to study evaluation, 6.0 years) had more joint pain (odds ratio for having joint pain in any joint, 2.1 [CI, 1.2 to 3.5]; P = 0.007), more symptoms of memory impairment (odds ratio for having any memory problem, 1.9 [CI, 1.1 to 3.5]; P = 0.003), and poorer functional status due to pain (odds ratio for 1 point on the SF-36 scale, 1.02 [CI, 1.01 to 1.03]; P < 0.001) than persons without previous Lyme disease. However, on physical examination, case-patients and controls did not differ in musculoskeletal abnormalities, neurologic abnormalities, or neurocognitive performance. Persons with previous Lyme disease who had persistent symptoms after receiving treatment (n = 67) were more likely than those who had completely recovered to have had fever, headache, photosensitivity, or neck stiffness during their acute illness (87% compared with 13%; odds ratio, 2.4 [CI, 1.0 to 5.5]; P = 0.045); however, the performance of the two groups on neurocognitive tests did not significantly differ.

CONCLUSIONS

Because persons with previous Lyme disease exhibited no sequelae on physical examination and neurocognitive tests a mean of 6.0 years after infection, musculoskeletal and neurocognitive outcomes seem to be favorable. However, long-term impairment of functional status can occur.

Neuropsychological deficits in Lyme disease patients with and without other evidence of central nervous system pathology

A small percentage of Lyme patients develop mild to moderate encephalopathic symptoms months to years after diagnosis and treatment. Their symptoms typically include fatigue, memory loss, sleep disturbance, and depression. However, the etiology of this syndrome remains controversial. It is generally thought that Lyme patients with abnormal cerebral spinal fluid (CSF) have a neurological basis to their illness. To further examine this question, we compared Lyme patients with evidence of abnormal CSF, intrathecal antibody to Borrelia burgdorferi, elevated protein, or a positive polymerase chain reaction for B. burgdorferi DNA (n = 14); Lyme patients with normal CSF (n = 18); and healthy controls (n = 15) on a battery of neuropsychological and personality tests. Although both Lyme groups reported memory problems, only the Lyme group with abnormal CSF had measurable memory deficits. Both Lyme groups had higher depression scores than the normal control group, although depression was not correlated with memory scores. It appears that Lyme patients with abnormal CSF may have a neurological basis to their illness, whereas affective symptoms, common to many chronic disorders, may predispose other Lyme patients to the perception of cognitive dysfunction.