Shawn J. Bird

Direct muscle stimulation in acute quadriplegic myopathy

We have previously found that muscle is electrically inexcitable in severe acute quadriplegic myopathy (AQM). In contrast, muscle retains normal electrical excitability in peripheral neuropathy. To study the relationship between muscle electrical excitability and all types of flaccid weakness occurring in the intensive care unit, we identified 14 critically ill, weak patients and measured the amplitude of compound muscle action potentials (CMAPs) obtained with direct muscle stimulation (dmCMAP) and with nerve stimulation (neCMAP). In 11 of 14 patients dmCMAP amplitudes were reduced and the ratio of the neCMAP amplitude to the dmCMAP amplitude (nerve/muscle ratio) was indicative of loss of muscle electrical excitability. In 2 other patients, the nerve/muscle ratio indicated neuropathy. Direct muscle stimulation may allow differentiation of AQM from neuropathy even in comatose or encephalopathic critically ill patients. AQM may be more common than has previously been appreciated.

Muscle is electrically inexcitable in acute quadriplegic myopathy

We directly stimulated muscle in three patients with acute quadriplegic myopathy to determine whether paralyzed muscle in this syndrome is electrically excitable. Two of the patients had been treated with neuromuscular blocking agents and corticosteroids, and one patient had been treated with corticosteroids alone. We found that paralyzed muscle is electrically inexcitable in affected patients. Muscle regained electrical excitability over weeks to months. The recovery of muscle excitability paralleled the clinical recovery of patients, suggesting that paralysis in this syndrome is secondary to electrical inexcitability of muscle membrane.

Critical Illness Myopathy

Acute myopathy is a common problem in intensive care units. Those at highest risk for developing critical illness myopathy are exposed to intravenous corticosteroids and paralytic agents during treatment of various illnesses. Diffuse weakness and failure to wean from mechanical ventilation are the most common clinical manifestations. Serum creatine kinase levels are variable. Electrodiagnostic studies reveal findings of a myopathic process, often with evidence of muscle membrane inexcitability. Based on animal model studies, the loss of muscle membrane excitability may be related to inactivation of sodium channels at the resting potential. In addition, human and animal pathologic studies reveal characteristic loss of myosin with relative preservation of other structural proteins. In some patients, there is also upregulation of proteolytic pathways, involving calpain and ubiquitin, in conjunction with increased apoptosis. Fortunately, the disorder is reversible, but there may be considerable morbidity.

Involvement of skeletal muscle in dialysis-associated systemic fibrosis (nephrogenic fibrosing dermopathy)

Nephrogenic fibrosing dermopathy (NFD), a newly recognized scleroderma‐like disease, was originally described as a purely cutaneous disorder. More widespread involvement, including fibrosis of pulmonary and cardiac tissues, has been documented only recently, and it has been suggested that a more appropriate designation is dialysis‐associated systemic fibrosis. We report five cases of this novel disorder, spanning a spectrum of primarily skin to primarily muscle involvement. Clinical, radiological, electrophysiological, and pathological studies revealed moderate to severe fibrosis of striated muscles. All patients had end‐stage renal failure on chronic dialysis, subacute to chronic hardening of the skin and muscles, restriction of limb movements with joint contractures, but normal to only mildly weak muscle strength. Limitation of movements was caused predominantly by skin tightness and induration, and by joint contractures rather than muscle weakness. Computerized tomography showed fibrosis of the fascia and muscles in the most severely affected patients, and electromyography showed mild to severe myopathic changes. Histopathology of affected muscles revealed a spectrum of mild to severe fibrosis, degenerating fibers, and chronic inflammatory cells. These results further support the contention that NFD is not a purely cutaneous disease, but is part of a larger systemic fibrotic process that may involve muscles. Muscle Nerve, 2004

Transcervical Thymectomy for Myasthenia Gravis Achieves Results Comparable to Thymectomy by Sternotomy

BACKGROUND It remains controversial whether transcervical thymectomy offers results equivalent to thymectomy by way of a median sternotomy in the treatment of myasthenia gravis. Furthermore, preoperative prognostic factors have not been clearly defined. METHODS This study is a retrospective chart review and interview of 78 patients completing transcervical thymectomy for myasthenia gravis between 1992 and 1999. RESULTS There were 24 men and 54 women. Mean age was 40 years (range, 13 to 78 years). Twelve patients were in Osserman class 1, 25 in class 2, 30 in class 3, and 11 in class 4 (mean, 2.5). There was no perioperative mortality and 6 (7.7%) morbidities. Mean length of stay was 1.5 days and mean follow-up, 54.6 months. The crude cumulative complete remission (asymptomatic off medications for 6 months) rate was 39.7% (n = 31). Only 8 patients (10.3%) failed to improve after transcervical thymectomy. Kaplan-Meier estimates of complete remission were 31% and 43% at 2 and 5 years, respectively. Eight patients with thymoma had a 5-year estimated complete remission rate of 75% in contrast to 43% in 38 patients with thymic hyperplasia and 36% in 32 patients with neither thymoma nor hyperplasia (p = 0.01). Twelve patients with ocular myasthenia had a 5-year estimated complete remission rate of 57%, whereas patients with mild-to-moderate (n = 55) or severe (n = 11) generalized symptoms had 5-year complete remission rates of 43% and 30%, respectively (p = 0.21). CONCLUSIONS Overall, extended transcervical thymectomy offers results that are comparable to those published for the transsternal procedure. Patients with milder disease (including isolated ocular disease) and taking no preoperative immunosuppressive agents appear to experience higher remission rates. In contrast to previous studies, we also find that small thymomas predict better responses to thymectomy.

Suprascapular neuropathy. Variability in the diagnosis, treatment, and outcome.

The functional outcome of operative and nonoperative treatment of suprascapular neuropathy was compared to determine the preferred method of treatment for each etiology of nerve injury. The predictive value of preoperative electromyography also was studied. Fifty-three patients were evaluated at least 1 year (average, 28 months) from the time of operative (n = 36) or nonoperative (n = 17) treatment. A modified American Shoulder and Elbow Surgeons self-assessment score was obtained at presentation and at final followup. Electromyography data were obtained at initial presentation. Minimal electromyographic changes associated with denervation were associated with a limited response to treatment, especially in patients with nerve compression secondary to spinoglenoid notch cysts. Pretreatment electromyographic findings, therefore, were predictive of treatment response. Overall, operative and nonoperative treatment of these suprascapular nerve injuries resulted in significant functional improvement, but the results varied depending on the etiology of the injury. Spinoglenoid notch cysts responded significantly better to operative treatment, with the results for open surgery being the same as the results for arthroscopic decompression. In addition, compressive lesions attributable to suprascapular notch entrapment had the best improvement with surgical decompression. Traumatic lesions, including traction and direct closed injuries, had an equal response to operative and nonoperative treatment. Overuse injuries did not improve with operative treatment. Viral neuritis improved with nonoperative treatment and never was treated with surgery. Overall, traumatic injuries resulted in significantly worse final outcomes than any other etiologic processes. In the nonoperative group, neuropathy secondary to spinoglenoid cysts resulted in significantly worse function. The outcome of treatment is dependent on the severity and etiology of the nerve injury, and the method of treatment.

Chronic inflammatory demyelinating polyneuropathy associated with malignant melanoma

We report three patients who developed chronic inflammatory demyelinating polyneuropathy (CIDP) in association with malignant melanoma. In two cases, melanoma was discovered during the initial evaluation for neuropathy. Two patients also had vitiligo, an antibody-mediated disorder that may complicate melanoma. Melanoma cells and Schwann cells are both of neuroectodermal cell origin, with shared surface antigens. Shared immunoreactivity may account for the association between melanoma and CIDP, as with vitiligo.

Clinical and electrophysiologic improvement in Lambert‐Eaton syndrome with intravenous immunoglobulin therapy

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Pseudo-conduction block in vasculitic neuropathy.

The predominant electrophysiologic feature of vasculitic mononeuropathy multiplex is axonal loss. Electrophysiologic findings interpreted as conduction block have, however, also been reported to occur in neuropathy secondary to necrotizing vasculitis. We report 3 patients with mononeuropathy multiplex and biopsy proven vasculitis in whom eight nerves met criteria for conduction block. In each circumstance, serial study demonstrated conversion of the electrophysiologic findings to those most consistent with severe axonal loss. “Conduction block” in vasculitic mononeuropathy multiplex is secondary to focal axonal conduction failure presumably related to infarctive axonal injury. The term conduction block should be used with caution in this disorder and only if serial studies demonstrate findings consistent with this electrophysiologic diagnosis.

brief communicationsL Corticosteroid‐responsive dominantly inherited neuropathy in childhood

We describe three children with corticosteroid-responsive inflammatory demyelinating polyneuropathy from families with dominantly inherited neuropathy. There were atypical clinical, electrophysiologic, and pathologic characteristics that suggested a coexistent inflammatory demyelinating neuropathy and that should alert the clinician to the possibility of an associated acquired, potentially treatable disorder.