From the Guidelines
Electromyography (EMG) plays a crucial role in the diagnosis of Stiff Person Syndrome, as it typically reveals continuous motor unit activity in affected muscles at rest, which is a hallmark finding of the condition. This continuous activity appears as involuntary firing of motor units that persists even when the patient attempts to relax completely. The abnormal EMG pattern shows simultaneous co-contraction of agonist and antagonist muscles, particularly in the lumbar paraspinal, abdominal, and proximal leg muscles. These contractions fail to be suppressed by voluntary effort but can be reduced or eliminated temporarily with intravenous diazepam administration, which serves as both a diagnostic feature and therapeutic approach.
Some of the provided evidence, such as the study on immune-related adverse events in patients treated with immune checkpoint inhibitor therapy 1, discusses the use of EMG in the context of myositis, but it is not directly relevant to Stiff Person Syndrome. However, the study highlights the importance of EMG in diagnosing muscle disorders. Another study on the diagnosis and management of Guillain-Barré Syndrome 1 mentions electrodiagnostic studies, including EMG, but again, it is not directly applicable to Stiff Person Syndrome.
A study on idiopathic inflammatory myopathies 1 discusses the use of EMG in diagnosing myopathic processes, which may be relevant to Stiff Person Syndrome, but it is not the most recent or directly relevant study.
Given the available evidence, the most important finding is that EMG is essential in diagnosing Stiff Person Syndrome, as it helps differentiate it from other neuromuscular disorders. The neurophysiological findings correlate with the clinical presentation of muscle rigidity and painful spasms that characterize the condition. These EMG findings support the diagnosis, especially when combined with serological testing for glutamic acid decarboxylase (GAD) antibodies, which are present in approximately 60-80% of cases.
Key points to consider:
- EMG is a crucial diagnostic tool in Stiff Person Syndrome
- Continuous motor unit activity in affected muscles at rest is a hallmark finding
- EMG helps differentiate Stiff Person Syndrome from other neuromuscular disorders
- Serological testing for GAD antibodies is also important in supporting the diagnosis
- The provided evidence, although not directly relevant in some cases, highlights the importance of EMG in diagnosing muscle disorders.
From the Research
Role of Electromyography (EMG) in Stiff Person Syndrome
- Electromyography (EMG) is used to diagnose and monitor Stiff Person Syndrome (SPS) by detecting continuous motor unit activity in agonist and antagonist muscles 2.
- EMG findings in SPS include continuous muscle activity that varies with awake and sleep states, posture, passive and active movements, and medications 3.
- The use of simultaneous video-electroencephalographic-surface electromyographic recordings can help confirm the diagnosis of SPS and define reproducible clinical and neurophysiologic criteria for the syndrome 3.
- EMG can help elucidate the clinical findings in SPS and can be used to monitor the effectiveness of treatment 3.
- The role of EMG in SPS is supported by studies that have used EMG to diagnose and monitor the condition, and to evaluate the response to treatment with medications such as diazepam, baclofen, and intravenous immunoglobulin 2, 3.