What does L. Peroneus (Left Peroneal) nerve finding of Fibs (Fibrillations) 1+ and PSW (Positive Sharp Waves) 1+ indicate in an EMG (Electromyography) study?

EMG Findings: Left Peroneal Nerve with Fibrillations 1+ and Positive Sharp Waves 1+

The presence of 1+ fibrillations and 1+ positive sharp waves in the left peroneal nerve distribution indicates mild denervation, suggesting active or recent nerve injury with muscle fiber denervation. This finding represents spontaneous electrical activity from denervated muscle fibers that have lost their normal nerve supply 1.

What These Findings Mean

Fibrillations and positive sharp waves are the electrophysiological hallmark of denervated skeletal muscle and represent spontaneous activity from individual muscle fibers that have lost their nerve connection 1.

Pathophysiology of These Findings

• Fibrillation potentials are spontaneously discharging muscle fibers seen as short duration muscle fiber action potentials (typically less than 5 ms in duration) with a regular pattern of discharge 1
• Positive sharp waves are also spontaneous short duration muscle fiber action potentials, always in the positive (downward) direction, with a regular discharge pattern 1
• Both findings are associated with denervation and indicate that muscle fibers have lost their normal nerve supply 1

Timing and Development

These spontaneous discharges typically develop approximately one week after nerve injury, not immediately 1:

• When an axon is first damaged and muscle fibers are denervated, spontaneous discharges usually only occur when muscle fibers are stimulated directly by needle movement 1
• Spontaneous activity (positive waves and fibrillations) begins to develop after about a week following denervation 1
• The presence of fibrillations at 18 hours after birth in a newborn with peroneal neuropathy suggested intrauterine onset, as these findings require time to develop 2

Clinical Significance of "1+" Grade

The "1+" grading indicates mild or minimal spontaneous activity, representing the lowest grade of abnormal spontaneous activity on the standard EMG grading scale 1:

• This suggests early, mild, or partial denervation rather than severe or complete nerve injury
• The finding indicates some degree of ongoing denervation but not extensive muscle fiber involvement
• Multiple criteria must be used and abnormalities must be concordant across several aspects when evaluating for neuropathy 1

Differential Diagnosis and Implications

Peripheral Nerve Injury Patterns

The left peroneal nerve is particularly vulnerable to injury due to its superficial course around the fibular head:

• Trauma or compression at the fibular head (most common)
• Stretch injury from positioning, weight loss, or leg crossing
• Systemic neuropathy affecting the peroneal nerve preferentially
• Intrauterine mechanisms in neonates, as demonstrated by the presence of fibrillations at birth 2

Important Diagnostic Considerations

An excellent prognosis for recovery includes a normal motor unit recruitment pattern with only a slightly decreased interference pattern and no fibrillation potentials or positive sharp waves 1. Therefore, the presence of these findings, even at 1+, suggests:

• Active denervation is occurring, indicating the nerve injury is recent or ongoing
• Recovery potential depends on the severity and whether reinnervation can occur
• Serial EMG examinations over time may be helpful to assess for progression or recovery 1

Prognostic Implications

A poor prognosis is defined as reduced motor unit recruitment with acute or chronic spontaneous activity 1:

• The presence of fibrillations and positive sharp waves, even at 1+, indicates some degree of denervation
• Over weeks to months, intact neighboring axons may sprout to reinnervate adjacent denervated muscle fibers, which would be seen as polyphasic potentials on follow-up EMG 1
• The 1+ grading suggests mild involvement, which generally carries a better prognosis than higher grades

Clinical Pitfalls to Avoid

Do not assume the absence of fibrillations and positive sharp waves rules out neuropathy in all cases 3:

• In some conditions like early ALS, patients may show no fibrillations but have profuse fasciculations with denervation-reinnervation changes 3
• The timing of the EMG relative to the injury is critical - fibrillations take approximately one week to develop after denervation 1
• Adequate sampling of insertional activity is essential to avoid missing focal abnormalities 1

Fibrillations and positive sharp waves can transform into each other and show atypical firing patterns, so the electromyographer must be experienced in recognizing these variations 4.