CPT® Code 95928

1. Indications

The central motor evoked potential study (CPT® Code 95928) is indicated for the evaluation of motor pathway function in the upper extremities. This procedure is typically performed in the following scenarios:

• Neurological Disorders Assessment of conditions such as multiple sclerosis, amyotrophic lateral sclerosis (ALS), or other demyelinating diseases that may affect motor pathways.
• Motor Function Evaluation Determining the integrity of motor pathways in patients with unexplained weakness or motor deficits in the upper limbs.
• Pre-Surgical Assessment Evaluating motor function prior to surgical interventions that may impact the motor pathways.
• Post-Trauma Evaluation Assessing motor function following traumatic brain injury or stroke to determine the extent of motor pathway involvement.

2. Procedure

The central motor evoked potential study involves several detailed procedural steps to ensure accurate assessment of motor pathway function:

• Baseline Nerve Conduction Studies Prior to the MEP recording, baseline nerve conduction studies of the upper extremities are performed to establish reference values for comparison during the evaluation.
• Electrode Placement Electrodes are placed on the skin over the appropriate muscles, typically including the biceps, triceps, abductor pollicis brevis, and abductor digiti minimi. The placement is crucial for obtaining accurate readings of muscle response.
• Impedance Check The impedances of the electrodes are checked to ensure they are within acceptable limits. Adjustments are made as necessary to optimize the quality of the recordings.
• Optimal Scalp Location Identification Starting with the abductor digiti minimi muscle, the optimal scalp location for electrical stimulation is identified for each muscle tested. This step is essential for eliciting the strongest possible motor response.
• MEP Threshold Determination The threshold for eliciting a motor evoked potential (MEP) is determined by gradually increasing the stimulation until a response is recorded.
• Cortex Stimulation and MEP Recording The motor area of the cerebral cortex is stimulated, and the MEPs are recorded. Key measurements include the amplitude or strength of the response and the onset latency, which are compared to the baseline nerve conduction study results.
• CMAP Testing The compound muscle action potential (CMAP) is tested by stimulating the ulnar nerve for the abductor digiti minimi muscle. The relative strength of the MEP response is measured as a percentage of the CMAP strength.
• Central Motor Conduction Time Calculation The central motor conduction time (CMCT) is calculated based on the recorded data, providing further insight into motor pathway function.
• Stimulator Output Adjustment The stimulator output is reduced in 5% increments to measure the dissociation between MEP threshold and the cortical stimulation silent period (CSSP). This helps in understanding the excitatory and inhibitory effects of transcranial stimulation.
• Data Replication and Storage The data is replicated to ensure accuracy, and the signals are stored for further analysis.
• Contralateral Testing The procedure is repeated on 3-4 muscles in the ipsilateral upper extremity, followed by testing the contralateral upper extremity in the same manner to provide a comprehensive evaluation.
• Physician Review Finally, the physician reviews the recordings and provides a written report of findings, which is essential for diagnosis and treatment planning.

3. Post-Procedure

After the completion of the central motor evoked potential study, the patient may be monitored briefly to ensure there are no immediate adverse effects from the stimulation. The physician will analyze the recorded data and compare it to the baseline nerve conduction studies to assess motor pathway integrity. The findings will be compiled into a detailed report, which will include the MEP amplitudes, onset latencies, CMAP results, and any observed dissociations between excitatory and inhibitory responses. This report is crucial for guiding further diagnostic or therapeutic interventions based on the patient's neurological status. Patients may resume normal activities following the procedure, but any specific post-procedure care or follow-up appointments will be determined by the physician based on the individual patient's needs and clinical context.