What is causing my new onset left arm and hand weakness, left outer toe cramping, and occasional fasciculations (muscle twitchings), given my history of fasciculations (muscle twitchings) 6 years ago, as a 43-year-old female?

Urgent Neurological Evaluation Required for Asymmetric Weakness

You need urgent medical evaluation, ideally within 24-48 hours, as new-onset unilateral arm and hand weakness with cramping requires immediate investigation to exclude serious neurological conditions including Guillain-Barré syndrome variants, nerve root compression, or other treatable causes. 1, 2

Why This Requires Urgent Attention

Your presentation is concerning because:

• Asymmetric weakness (affecting only the left side) is atypical for benign fasciculation syndrome, which typically causes twitching without true weakness 1
• New motor weakness represents a significant change from your prior fasciculations alone, suggesting possible nerve or nerve root pathology 1
• Cramping in specific toes combined with arm weakness suggests a pattern that could represent multiple nerve involvement (mononeuritis multiplex) or nerve root compression 1
• Approximately 20% of Guillain-Barré syndrome patients can present with asymmetric patterns initially, and this condition can progress to respiratory failure requiring urgent monitoring 2

Immediate Diagnostic Workup Needed

Your physician should order:

Priority #1: MRI of Entire Spine

• MRI of cervical, thoracic, and lumbar spine without and with contrast is the critical first test to exclude spinal cord compression, nerve root compression (such as cervical radiculopathy causing arm weakness), or inflammatory conditions like transverse myelitis 2
• This imaging must be done urgently because spinal cord or nerve root compression requires immediate intervention to prevent permanent damage 2

Priority #2: Nerve Conduction Studies and EMG

• Electrodiagnostic testing can distinguish between nerve root problems, peripheral nerve entrapment (like ulnar nerve at elbow), polyneuropathy, or polyradiculoneuropathy patterns seen in Guillain-Barré syndrome 1, 2, 3
• These studies show whether the problem is demyelinating (nerve coating damage) or axonal (nerve fiber damage), which guides treatment 3
• For polyneuropathy, studies show diffuse abnormalities with relatively uniform involvement, while focal problems show localized changes 1

Priority #3: Cerebrospinal Fluid Analysis

• CSF analysis (spinal tap) may be needed if imaging and nerve studies suggest Guillain-Barré syndrome or inflammatory polyradiculoneuropathy 2
• This test shows elevated protein with normal cell count in Guillain-Barré syndrome 2

What Your Symptoms Suggest

Most Likely Possibilities:

Cervical Radiculopathy (Nerve Root Compression)

• Left arm and hand weakness with specific distribution suggests possible C6-C8 nerve root involvement 2
• Toe cramping could represent separate L5-S1 involvement or referred symptoms 1
• This is treatable and often improves with conservative management or surgical decompression if severe 2

Mononeuritis Multiplex

• Asymmetric involvement of multiple individual nerves can present with weakness in one arm and cramping in specific toes 1
• This pattern requires investigation for underlying causes including vasculitis, diabetes, or inflammatory conditions 1
• The American College of Rheumatology defines this as affecting multiple individual nerves in an asymmetric pattern 1

Guillain-Barré Syndrome Variant

• While typically symmetric and ascending from legs, approximately 20% can have atypical presentations including asymmetric patterns 2
• Your history of fasciculations 6 years ago that resolved makes this less likely but doesn't exclude it 2
• This requires urgent treatment with IVIG or plasmapheresis if confirmed 2

Less Likely But Must Exclude:

Ulnar Nerve Entrapment

• Can cause hand and arm weakness, particularly affecting 4th and 5th fingers 3
• MRI or ultrasound can diagnose this with high accuracy (sensitivity 77-79%, specificity 94-98%) 3

Functional Neurological Disorder

• Can present with weakness and sensory symptoms that are inconsistent with anatomical patterns 4, 5
• However, this is a diagnosis of exclusion only after structural and inflammatory causes are ruled out 4

Critical Red Flags Requiring Emergency Department Visit

Go to the emergency department immediately if you develop:

• Difficulty breathing or shortness of breath (suggests respiratory muscle involvement) 2
• Difficulty swallowing or speaking (suggests bulbar involvement) 2
• Weakness spreading to the right side or legs (suggests progressive process) 2
• Loss of bladder or bowel control (suggests cauda equina syndrome requiring emergency surgery) 2
• Severe pain radiating down arm or leg (suggests nerve root compression) 2

What NOT to Do While Awaiting Evaluation

• Do not delay seeking medical attention thinking this will resolve on its own like your previous fasciculations 2
• Do not assume this is benign fasciculation syndrome since you now have true weakness, not just twitching 1
• Do not wait for symptoms to worsen before seeking evaluation, as some conditions require early intervention to prevent permanent damage 2

Regarding Your Previous Fasciculations

Your history of fasciculations 6 years ago that improved after 6 months was likely benign fasciculation syndrome, which causes muscle twitching without weakness 1. However, the key difference now is that you have actual weakness and cramping, not just twitching 1. This represents a new and different problem requiring investigation.

Benign fasciculation syndrome does not cause:

• Progressive weakness 1
• Asymmetric motor deficits 1
• Loss of function 1

Bottom Line

Schedule an urgent neurology appointment or visit your primary care physician within 24-48 hours for immediate referral and diagnostic workup. 2 The combination of new unilateral weakness and cramping requires systematic investigation with MRI spine and electrodiagnostic studies to identify the cause and initiate appropriate treatment before any potential progression occurs. Most causes are treatable, especially when identified early.