Upper Motor Neuron (UMN): Lesions occur proximal to the anterior horn cell within the brain or spinal cord, typically affecting the corticospinal tract.
Lower Motor Neuron (LMN): Lesions occur distal to the anterior horn cell, affecting peripheral nerves after they leave the spinal cord to innervate skeletal muscle.

⚖️ Comparison of UMN and LMN Signs

Feature	UMN	LMN
Weakness	✔️ Yes	✔️ Yes
Reflexes	⬆️ Hyperreflexia	⬇️ Hyporeflexia / absent
Plantar Reflex	Extensor (upgoing) → Babinski sign 👣	Flexor (downgoing)
Muscle Tone	Increased (spasticity)	Decreased (flaccidity)
Muscle Wasting	Minimal (disuse atrophy)	Significant (denervation atrophy)
Fasciculations	Absent ❌	Present ✅ (twitching)

🧩 Causes of UMN Signs

🧠 Stroke: Ischaemic or haemorrhagic → classically contralateral hemiparesis.
🎗️ Brain Tumour: Compressing motor cortex or corticospinal tracts.
🌀 Multiple Sclerosis: Demyelination in CNS → patchy UMN findings.
🚑 Spinal Cord Trauma: Cervical cord lesions → quadriparesis, spasticity.
🧬 Motor Neuron Disease (ALS): Mixed UMN + LMN features.

⚡ Causes of LMN Signs

🔧 Peripheral Nerve Damage: Trauma, compression (e.g., carpal tunnel).
🍺 Peripheral Neuropathy: Diabetes, alcohol, toxins, chemotherapy.
🦠 Polio: Viral destruction of anterior horn cells.
🛡️ Guillain–Barré Syndrome: Acute demyelination of peripheral nerves.
🧬 Motor Neuron Disease (ALS): LMN involvement with fasciculations + wasting.

🔀 Conditions with Both UMN and LMN Signs

🥩 Vitamin B12 Deficiency: Subacute combined degeneration → spastic paraparesis + neuropathy.
🦠 Taboparesis (Syphilitic Myelopathy): Late neurosyphilis → mixed picture.
🧬 ALS (Motor Neuron Disease): Mixed UMN + LMN in different muscle groups.
🧬 Friedreich’s Ataxia: Genetic, affects spinal cord + cerebellum.
🐎 Cauda Equina Lesions: Mostly LMN, but mixed in complex compression syndromes.

💡 Clinical Pearls

UMN signs usually localise to the brain/spinal cord, while LMN signs suggest peripheral nerve or anterior horn cell disease.
Fasciculations are a hallmark of LMN involvement (denervation).
Babinski sign 👣 is classic for UMN lesions.
ALS uniquely presents with a combination of UMN + LMN features in different regions.

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Upper and Lower Motor Neuron signs

🧠 Anatomy

⚖️ Comparison of UMN and LMN Signs

🧩 Causes of UMN Signs

⚡ Causes of LMN Signs

🔀 Conditions with Both UMN and LMN Signs

💡 Clinical Pearls

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