Plasticity of the human motor system following muscle reconstruction: a magnetic stimulation and functional magnetic resonance imaging study

OBJECTIVE

Although motor system plasticity in response to neuromuscular injury has been documented, few studies have examined recovered and functioning muscles in the human. We examined brain changes in a group of patients who had a muscle transfer.

METHODS

Transcranial magnetic stimulation (TMS) was used to study a unique group of 9 patients who had upper extremity motor function restored using microneurovascular transfer of the gracilis muscle. The findings from the reconstructed muscle were compared to the homologous muscle of the intact arm. One patient was also studied with functional magnetic resonance imaging (fMRI).

RESULTS

TMS showed that the motor threshold and short interval intracortical inhibition was reduced on the transplanted side while at rest but not during muscle activation. The difference in motor threshold decreased with the time since surgery. TMS mapping showed no significant difference in the location and size of the representation of the reconstructed muscle in the motor cortex compared to the intact side. In one patient with reconstructed biceps muscle innervated by the intercostal nerves, both TMS mapping and fMRI showed that the upper limb area rather than the trunk area of the motor cortex controlled the reconstructed muscle.

CONCLUSIONS

Plasticity occurs in cortical areas projecting to functionally relevant muscles. Changes in the neuronal level are not necessarily accompanied by changes in motor representation. Brain reorganization may involve multiple processes mediated by different mechanisms and continues to evolve long after the initial injury.

SIGNIFICANCE

Central nervous system plasticity following neuromuscular injury may have functional relevance.

Clinical experience with 20 cases of group A streptococcus necrotizing fasciitis and myonecrosis: 1995 to 1997

During the last decade, there has been a dramatic resurgence of necrotizing fasciitis caused by group A streptococcal disease with mortality rates from 43 to 58 percent. The objective of this study was to review recent clinical experience regarding the diagnosis and management of streptococcal necrotizing fasciitis, including the use of high-dose intravenous immunoglobulin. From April of 1995 to December of 1997, 20 consecutive adult patients meeting clinical and/or histopathologic criteria for streptococcal necrotizing fasciitis were identified in the Toronto area. Of those, 16 (80 percent) were treated with > or = 1 mg/kg of intravenous immunoglobulin. Fourteen men and 6 women ranging in age from 33 to 89 were identified (median age 55.5 years). Sixteen patients (80 percent) with necrotizing fasciitis survived. Ten patients had necrotizing fasciitis alone, none of whom died. Eight patients were identified with myonecrosis and necrotizing fasciitis, three of whom died. The case fatality rate of all patients who received intravenous immunoglobulin was 19 percent (3 of 16) and was not statistically significantly different (p = 1.0) from the case fatality rate of 25 percent (1 of 4) in those patients who did not receive intravenous immunoglobulin. A total of seven patients (35 percent) were diagnosed as having a cause for their signs and symptoms other than necrotizing fasciitis when they initially presented to a physician; one of these patients died. There was no correlation with the M type or the streptococcal pyrogenic exotoxin genotype and outcome.