Laughlin, Ruple S.

ABSTRACT Introduction Existing normal value references for pediatric nerve conduction studies (NCS) are based on limited sample sizes with uncertain reliability, suggesting a need for better normative data. Methods Electronic medical records were reviewed for pediatric patients (0 to <18 years) with normal findings on electromyography and NCS during the period from January 1, 1997 through September 20, 2017. Electrodiagnostic and demographic data were collected. Gaussian and descriptive statistics were used to establish normal values by age group. Results In this study we analyzed 1,918 normal NCS on 1,849 unique pediatric patients. Patients were stratified by age: 0 to <1 month; 1 to <6 months; 6 to <12 months; 12 to <24 months; 2 to <3 years; 3 to <4 years; 4 to <5 years; 5 to <10 years; 10 to <15 years; and 15 to <18 years. Normal reference ranges for amplitude, conduction velocity, and distal latency were established for each age group for 4 motor and 4 sensory nerves. Discussion The large sample size of this study provides reliable reference values for interpreting pediatric NCS. Muscle Nerve 60 : 155–160, 2019

ABSTRACTIntroductionNeuropathy after total knee arthroplasty (TKA) can cause significant morbidity but is inconsistently reported.MethodsWe reviewed the clinical, electrodiagnostic and perioperative features of all patients who underwent primary TKA at our institution and developed a new neuropathy within 8 weeks postoperatively.ResultsFifty‐four cases were identified (incidence 0.37% [95% confidence interval, 0.28–0.49]) affecting the following nerve(s): peroneal (37), sciatic (11), ulnar (2), tibial (2), sural (1), and lumbosacral plexus (1). In all cases with follow‐up data, motor recovery typically occurred within 1 year and was complete or near‐complete.ConclusionsPost‐TKA neuropathy is uncommon, typically does not require intervention and usually resolves within 1 year. Post‐TKA neuropathy most often affects the nerves surgically at risk. Anesthesia type does not correlate with post‐TKA neuropathy. An inflammatory etiology for post‐TKA neuropathy is rare but should be considered in specific cases. Muscle Nerve 59:679–682, 2019

ABSTRACTIntroduction: Decremental responses in repetitive nerve stimulation have been reported in a few hereditary myopathies. We examined the frequency of decrement in a cohort of myopathy patients. Methods: We reviewed all patients referred for myopathy who underwent repetitive nerve stimulation between January 2007 and May 2017. We included patients with decrement (>10%) and either a pathological or molecular diagnosis of myopathy. Results: Among 157 patients with myopathies, 4 patients had decrement (2 hydroxychloroquine‐associated vacuolar myopathy, 1 centronuclear myopathy, and 1 distal myopathy). One hydroxychloroquine‐associated vacuolar myopathy patient also had inflammatory myopathy. Pyridostigmine improved weakness in the centronuclear myopathy patient, but not in the distal myopathy patient. No patient with an acquired myopathy received pyridostigmine. Conclusions: Despite the rare occurrence of decrement in myopathy, its presence may urge consideration of pharmacological intervention. Muscle Nerve 59:475–478, 2019

ABSTRACT Introduction Needle electromyography (EMG) findings help confirm myopathy and may indicate specific pathologic changes on muscle biopsy. Methods We conducted a retrospective chart review of 218 consecutive patients referred for muscle biopsy. Presence of specific needle EMG findings was correlated with pathologic findings of inflammation, necrosis, splitting, and vacuolar changes. Sensitivity, specificity, and positive and negative predictive values of specific EMG findings for pathologic changes were calculated. Results Short‐duration motor unit potentials (MUP) were sensitive (83%–94%) but not specific (34%–49%) for pathologic changes. Fibrillation potentials were 65%–74% sensitive and 58%–81% specific for inflammation, necrosis, splitting, or vacuolar changes. The absence of fibrillation potentials had high negative predictive value (82%–93%) for inflammation, splitting, or vacuolar changes. Discussion Fibrillation potentials and short‐duration MUPs predict pathologic changes of muscle fiber necrosis, splitting, and/or vacuolar changes (as seen with inflammatory myopathies and muscular dystrophies). Absence of fibrillation potentials suggests other myopathologic changes (e.g., congenital myopathy). Muscle Nerve 59 :315–320, 2019

Background and purposeCACNA1S encodes Cav1.1, a voltage sensor for muscle excitation−contraction coupling, which activates the ryanodine receptor 1 (RYR1) leading to calcium release from the sarcoplasmic reticulum. CACNA1S mutations cause hypokalemic periodic paralysis, malignant hyperthermia and congenital myopathy. RYR1 mutations result in congenital myopathy, malignant hyperthermia and rhabdomyolysis.MethodsThe aim was to describe a novel phenotype associated with a CACNA1S variant at a site previously linked to hypokalemic periodic paralysis.ResultsThe patient presented with fluctuating asymptomatic creatine kinase elevation after an episode of rhabdomyolysis but has no history of periodic paralysis. His muscle biopsy showed core‐like structures occurring mainly in type 2 fibers. He carries a novel Cav1.1 variant (p.Arg528Leu) affecting a highly conserved amino acid. Different mutations at the same location cause hypokalemic periodic paralysis.ConclusionThis case underscores the similarity between the phenotypes caused by mutations in two functionally linked proteins, RYR1 and Cav1.1.

AbstractBackgroundCongenital myopathies due to ryanodine receptor (RYR1) mutations are increasingly identified and correlate with a wide range of phenotypes, most commonly that of malignant hyperthermia susceptibility and central cores on muscle biopsy with rare reports of distal muscle weakness, but in the setting of early onset global weakness.MethodsWe report a case of a patient presenting with childhood onset hand stiffness and adult onset progressive hand weakness and jaw contractures discovered to have two variants in the RYR1 gene.ResultsThe patient manifested with distal upper limb weakness which progressed to involve the distal lower limb, proximal upper limb, as well as the face in addition to limited jaw opening. Creatine kinase was mildly elevated with EMG findings supporting a myopathy. Muscle biopsy showed features consistent with centronuclear myopathy. Whole exome sequencing revealed a novel heterozygous pathogenic variant in RYR1 (c.12315_12328delAGAAATCCAGTTCC, p.Glu4106Alafs*8), and a heterozygous missense variant (c.10648C>T, p.Arg3550Trp) of unknown significance in compound heterozygous state.ConclusionWe expand the spectrum of RYR1‐related myopathy with the description of a novel phenotype in an adult patient presenting with hand weakness and suggest considering RYR1 analysis in the diagnosis of distal myopathies.

ABSTRACTIntroductionSjögren syndrome is thought to be a lymphocyte‐driven process. Peripheral nervous system involvement occurs in about 20%–25% of patients. A sensory‐predominant, large‐fiber peripheral neuropathy is most common, and it is usually associated with a subacute to chronic presentation.MethodsWe report a rare case of an acute Sjögren‐associated, sensory predominant, length‐dependent peripheral neuropathy mimicking Guillain–Barré syndrome. The patient presented with sensory ataxia preceded by fever and polyarthralgia. She gave a history of years of dry eyes and dry mouth.ResultsShe had a positive Shirmer test, abnormal salivary gland scan, and positive SS‐A and SS‐B antibodies. A sural nerve biopsy showed an unusual, dense, non‐IgG4, polyclonal, plasma‐cell perivascular infiltrate. The patient responded to treatment with weekly pulse intravenous methylprednisolone.ConclusionsSjögren syndrome can present with acute‐onset, sensory predominant peripheral neuropathy. The role of plasma cells in Sjögren syndrome is unexplored and deserves further study. Muscle Nerve 55: 605–608, 2017

ABSTRACTIntroduction: Fluoxetine is a selective serotonin reuptake inhibitor and long‐lived open channel blocker of the acetylcholine receptor, often used in the treatment of slow‐channel congenital myasthenic syndromes (CMS). Methods: We report a 42‐year‐old woman who had a history of episodic limb weakness that worsened after initiation of fluoxetine for treatment of depression. Genetic testing for CMS revealed a homozygous pathogenic mutation in the rapsyn (RAPSN) gene (p.Asn88Lys). Electrodiagnostic testing was performed before and 1 month after discontinuation of fluoxetine. Results: The 2 Hz repetitive nerve stimulation of the fibular and spinal accessory nerves showed a baseline decrement of 36% and 14%, respectively. One month after discontinuing fluoxetine, the spinal accessory nerve decrement was no longer present, and the decrement in the fibular nerve was improved at 17%. Conclusions: This case demonstrates worsening of both clinical and electrophysiologic findings in a patient with CMS secondary to a RAPSN mutation treated with fluoxetine. Muscle Nerve 55: 131–135, 2017