Nerve Conduction Studies in SLE: Findings and Management
Nerve conduction studies (NCS) in SLE patients are essential diagnostic tools that can identify peripheral neuropathies, differentiate between mononeuropathy and polyneuropathy, and distinguish axonal from demyelinating neuropathies, with management typically involving glucocorticoids and immunosuppressive therapy for confirmed SLE-related neuropathies. 1
Findings in Nerve Conduction Studies in SLE
Common NCS Abnormalities
- Polyneuropathy: Occurs in approximately 21% of SLE patients, defined as NCS abnormalities in two or more nerves 2, 3
- Axonal neuropathies: Most common pattern, typically presenting as length-dependent sensorimotor axonopathy 4
- Subclinical abnormalities: SLE patients without clinical neuropathy may show early nerve function changes compared to healthy controls, including:
- Lower amplitudes for ulnar, fibular, and tibial compound muscle action potentials (CMAP)
- Lower sural sensory nerve action potentials (SNAP)
- Slower conduction velocities in median, ulnar, and fibular motor nerves
- Slower conduction velocities in median, ulnar, and sural sensory nerves
- Longer minimum F-wave latencies 5
Small-Fiber Neuropathy
- Approximately 13% of SLE patients may have small-fiber neuropathy with reduced intraepidermal nerve fiber density
- This can occur despite normal NCS results, as conventional NCS primarily evaluates large-diameter nerve fibers 6
- Skin biopsy showing loss of intraepidermal nerve fibers may be necessary for diagnosis when electrodiagnostic studies are normal 1
Longitudinal Changes
- NCS parameters may fluctuate over time in individual patients
- Impairments are not necessarily irreversible, with 67% of NCS parameters remaining stable over a 7-year period 4
- A modest progressive neuropathic process exists in some SLE patients 4
Diagnostic Approach
When to Perform NCS
- In SLE patients presenting with:
- Altered sensation
- Pain
- Muscle weakness or atrophy 1
Comprehensive Evaluation
Exclude CNS involvement with neuroimaging when patients present with:
- Focal neurological signs
- Gait disturbance
- Visual or urinary disorders
- Increased tendon reflexes and/or muscle tone 1
Electrodiagnostic studies:
- NCS to identify mononeuropathies vs. polyneuropathies
- Needle electromyography to complement NCS findings
- Use quantifiable measures such as:
- Neuropathy Symptom Score (NSS)
- Neurological Disability Score (NDS)
- Vibration thresholds (VT) 2
Additional testing:
- CSF analysis for inflammatory demyelinating polyradiculoneuropathy
- Nerve biopsy (rarely needed)
- Skin biopsy when small-fiber neuropathy is suspected despite normal NCS 1
Management of SLE-Related Peripheral Neuropathies
First-Line Treatment
- Glucocorticoids alone or with immunosuppressive therapy:
For Severe or Refractory Cases
- Intravenous immunoglobulin
- Plasma exchange
- Rituximab 1
Monitoring
- Regular follow-up with repeat NCS to assess treatment response
- Quantifiable measures (NSS, NDS, VT) are useful for monitoring progress 2
- Monitor for general SLE activity as peripheral neuropathy has been reported to be a significant predictor of damage in SLE 1
Special Considerations
Antiphospholipid Antibodies
- Patients with antiphospholipid antibodies may require anticoagulation or antiplatelet therapy, especially if neuropathy is associated with vascular events 7
Pitfalls to Avoid
- Misdiagnosis: Neuropathic symptoms show poor correlation with NCS and VT; clinical diagnosis alone is insufficient 2
- Incomplete evaluation: Relying solely on NCS may miss small-fiber neuropathy 6
- Overtreatment: Not all NCS abnormalities require aggressive immunosuppression, as some may fluctuate or remain stable over time 4
- Delayed treatment: Early intervention is important as peripheral neuropathy can predict SLE damage 1
By using a systematic approach to diagnosis and management, peripheral neuropathies in SLE patients can be effectively identified and treated, potentially preventing long-term neurological damage.