Makindo Medical Notes

⚡ Fasciculations are spontaneous, involuntary contractions of groups of muscle fibres within a motor unit. They appear as visible "muscle twitches" under the skin. 👉 Often benign, but may indicate serious neurological disease (e.g., motor neuron disease).

📖 About

• Fasciculations result from spontaneous depolarisation of a lower motor neuron or its axon, causing visible twitches in the corresponding muscle fibres.
• Unlike fibrillations (seen only on EMG), fasciculations are visible to the naked eye.
• They can occur in health (benign fasciculations) or disease (neurological disorders).

🧬 Physiology

• Arise from hyperexcitability of motor neurons or instability of their axons.
• Triggered by spontaneous depolarisation of the anterior horn cell or its axon branch.
• Muscle twitches are irregular and not strong enough to cause joint movement.

🧠 Aetiology

🔍 Clinical Features

• Visible twitching under skin (esp. calves, thighs, eyelids, tongue).
• Usually painless, may cause discomfort or cramps.
• In benign fasciculation syndrome → no progression to weakness.
• In serious disease (e.g., MND) → associated with wasting, weakness, and mixed UMN/LMN signs.

🔬 Investigations

• 🧪 Bloods: Electrolytes (Ca, Mg, K), TFTs, LFTs, glucose, CK.
• 🧲 Neuroimaging: MRI spine if radiculopathy suspected.
• 📊 EMG (Electromyography): Fasciculations with denervation/reinnervation changes suggest MND.
• 💉 Autoimmune/serology: if systemic neuromuscular disorder suspected.

🛠️ Management

• ✅ Treat underlying cause: Correct electrolytes, adjust medications, manage thyroid disease.
• 🧘 Reassurance: Benign fasciculations often linked to stress/caffeine → lifestyle advice.
• 💊 Neurological disease: If associated with weakness/atrophy, refer urgently to neurology (exclude MND).
• 📅 Follow-up: Monitor progression; benign fasciculations are stable, while pathological ones progress.

🧑‍⚕️ Exam Teaching Pearl

🌟 Fasciculations = twitching (think MND if progressive). 〰️ Myokymia = rippling (often benign eyelid twitch or post-radiation nerve injury). 👉 Always check for weakness, wasting, UMN signs, and progression to separate benign from pathological causes.

🚩 Red Flags

• Progressive weakness or wasting.
• Bulbar symptoms (dysarthria, dysphagia).
• Mixed upper + lower motor neuron signs.
• Rapid progression or family history of MND/neuropathy.

🧑‍⚕️ Case Scenarios

✅ Conclusion

Fasciculations are common and often benign 🌟, but may signal serious disease such as MND ⚠️. A structured approach — history, examination, and targeted investigations — helps distinguish harmless twitches from progressive neurological pathology. Always assess for red flags (weakness, wasting, UMN signs) and refer when in doubt.