From the Guidelines
Temporal dispersion in nerve conduction studies (NCS) is a critical indicator of demyelination, particularly in acquired demyelinating neuropathies, and its management involves identifying the underlying cause and administering immunomodulatory therapies. When managing patients with temporal dispersion, clinicians should first identify the underlying cause through comprehensive neurological examination and additional testing, as seen in Guillain-Barré syndrome (GBS) where electrodiagnostic studies reveal a sensorimotor polyradiculoneuropathy or polyneuropathy, indicated by reduced conduction velocities, reduced sensory and motor evoked amplitudes, abnormal temporal dispersion and/or partial motor conduction blocks 1. Some key points to consider in the management of temporal dispersion include:
- Identifying the underlying cause, such as GBS, chronic inflammatory demyelinating polyneuropathy (CIDP), or multifocal motor neuropathy (MMN)
- Utilizing immunomodulatory therapies, such as intravenous immunoglobulin (IVIG) or plasma exchange, as treatment options
- Monitoring treatment response through regular follow-up NCS, with improvement in temporal dispersion suggesting effective therapy
- Considering maintenance therapies, like IVIG or subcutaneous immunoglobulin, for long-term management of conditions like CIDP Temporal dispersion occurs because demyelination affects nerve fibers unevenly, causing variable conduction velocities and resulting in phase cancellation and abnormal dispersion of the compound muscle action potential (CMAP), which helps differentiate demyelinating from axonal neuropathies, crucial for proper diagnosis and treatment selection, as noted in the diagnosis and management of GBS 1.
From the Research
Clinical Significance of Temporal Dispersion in NCS
- Temporal dispersion in nerve conduction studies (NCS) is a significant parameter in diagnosing demyelinating neuropathies 2, 3.
- It is characterized by a prolongation of the duration of compound muscle action potentials (CMAPs) and can be distinguished from conduction block by warming the limb, which increases the number of blocked nerve fibers and decreases temporal dispersion 4.
- Abnormal temporal dispersion is an important electrophysiological parameter for demyelination, and different criteria should be used for conduction block or abnormal temporal dispersion for a given nerve 5.
Management of Temporal Dispersion in NCS
- The management of temporal dispersion in NCS involves the use of electrodiagnostic criteria to distinguish between immune-mediated demyelination and compression-induced damage 6.
- Parameters such as distal compound muscle action potential duration, reduction of forearm motor conduction velocity, prolongation of minimum F-wave latency, and abnormal temporal dispersion can be used to diagnose immune-mediated demyelination 6.
- The use of modified electrodiagnostic criteria can improve the sensitivity and specificity of diagnosing immune-mediated demyelination, even in patients with extremely prolonged distal median motor latency 6.
Diagnostic Criteria for Temporal Dispersion
- Diagnostic criteria for conduction block and abnormal temporal dispersion have been proposed, including a more than 20% drop in peak-to-peak amplitude with less than a 10% change in negative-peak duration 5.
- However, these criteria may not be applicable to all nerves, and different criteria should be used for conduction block or abnormal temporal dispersion for a given nerve 5.
- The use of optimal cut-off values, such as a distal compound muscle action potential duration of ≥ 8 ms or a reduction of forearm motor conduction velocity by ≥ 30%, can improve the diagnosis of immune-mediated demyelination 6.