Makindo Medical Notes Comprehensive Medical Encyclopedia | Education for Healthcare Professionals

⚡ 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

Category	Examples	Key Clues
✅ Benign causes	Fatigue, stress, caffeine excess, exercise, anxiety	Intermittent, not progressive, no weakness/atrophy
🧪 Metabolic	Electrolyte imbalance (low Mg, Ca, K), thyroid disease	Associated with cramps, systemic symptoms
💊 Drugs	Cholinesterase inhibitors, corticosteroids, lithium	History of new medications, resolves if drug stopped
🧩 Neurological	Motor neuron disease (MND / ALS) Peripheral neuropathy Radiculopathy (compressed nerve root)	Persistent, associated with weakness, wasting, UMN signs (MND), sensory loss (neuropathy/radiculopathy)
⚠️ Other	Spinal cord lesions, neuromuscular junction disorders (rare)	Additional neurological features

🔍 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

Case 1: 22-year-old student, stressed before exams, notes eyelid twitching for 2 weeks. No weakness, normal exam. 👉 Likely benign fasciculations (stress/caffeine related). Reassure, reduce caffeine.

Case 2: 60-year-old man with calf twitches, weight loss, weakness, and wasting of small hand muscles. Fasciculations on tongue. 👉 Suspect Motor Neuron Disease (MND). Urgent neurology referral.

Case 3: 45-year-old woman with unilateral leg fasciculations, pain radiating from back, reduced ankle reflex. 👉 Likely lumbar radiculopathy. Arrange MRI lumbar spine.

✅ 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.

Fasciculation