3.5 Peripheral Neuropathies & Upper vs Lower Motor Neuron Signs
Key Takeaways
- Upper motor neuron (UMN) lesions produce spasticity, hyperreflexia, clonus, a positive Babinski sign, and minimal atrophy; lower motor neuron (LMN) lesions produce flaccidity, hyporeflexia or areflexia, marked atrophy, and fasciculations.
- Bell's palsy is an acute lower motor neuron lesion of the facial nerve (cranial nerve VII) causing one-sided facial weakness including the forehead; PTA care addresses facial exercises, eye protection, and education.
- Carpal tunnel syndrome compresses the median nerve at the wrist, causing thumb-side hand paresthesias; conservative care includes neutral-wrist night splinting, nerve gliding, and ergonomic education.
- Diabetic peripheral neuropathy produces a stocking-glove sensory loss, so daily foot inspection, proper footwear, and skin-protection education are essential PTA teaching points.
- Determining whether signs are UMN or LMN guides intervention selection and is a frequently tested NPTE-PTA reasoning skill.
Upper vs Lower Motor Neuron Lesions
The motor pathway has two parts. The upper motor neuron (UMN) runs from the brain (motor cortex) down through the spinal cord. The lower motor neuron (LMN) runs from the anterior horn of the spinal cord (or a cranial nerve nucleus) out to the muscle. A lesion's location produces a distinct, predictable sign pattern — and the NPTE-PTA tests whether you can read it.
| Sign | Upper Motor Neuron (UMN) Lesion | Lower Motor Neuron (LMN) Lesion |
|---|---|---|
| Muscle tone | Increased — spasticity | Decreased — flaccidity / hypotonia |
| Deep tendon reflexes | Increased — hyperreflexia | Decreased or absent — hyporeflexia / areflexia |
| Clonus | Often present | Absent |
| Babinski sign | Positive (great toe extends) | Negative (normal flexor response) |
| Muscle atrophy | Minimal (disuse only, develops slowly) | Marked and early |
| Fasciculations | Absent | Present |
| Weakness pattern | Groups of muscles, often distal | Specific muscles of the affected nerve/root |
| Examples | Stroke, spinal cord injury, traumatic brain injury, multiple sclerosis | Peripheral nerve injury, Guillain-Barre syndrome, polio, cauda equina, Bell's palsy |
Note that ALS is unusual — it damages both UMN and LMN, so a patient can show spasticity and hyperreflexia alongside atrophy and fasciculations.
Bell's Palsy
Bell's palsy is an acute lower motor neuron lesion of the facial nerve (cranial nerve VII), often idiopathic or viral. It causes sudden, one-sided facial weakness, and — because it is an LMN lesion — the entire half of the face, including the forehead, is affected (a central/UMN facial lesion spares the forehead). Findings include inability to close the eye, drooping mouth, loss of the nasolabial fold, and difficulty with facial expression. Most cases recover.
PTA-implemented care: gentle facial-muscle exercises and neuromuscular re-education, soft-tissue techniques, and patient education. Eye protection is critical — because the eye may not close, the patient is taught about lubricating drops, an eye patch, or taping the lid during sleep to prevent corneal damage.
Carpal Tunnel Syndrome (CTS)
Carpal tunnel syndrome (CTS) is compression of the median nerve beneath the transverse carpal ligament at the wrist. Symptoms include paresthesia and numbness in the thumb, index, middle, and the radial half of the ring finger, often worse at night, plus thenar weakness in advanced cases. Phalen, Tinel, and carpal compression tests provoke symptoms.
Conservative PTA-implemented care: neutral-wrist night splinting, median nerve and tendon gliding exercises, ergonomic and activity-modification education, and modalities within the plan of care.
Diabetic Peripheral Neuropathy
Diabetic peripheral neuropathy is nerve damage from chronically elevated blood glucose, producing a symmetrical, distal stocking-glove sensory loss that begins in the feet. The danger is loss of protective sensation — a patient cannot feel an injury, blister, or ill-fitting shoe, which can progress to ulceration and amputation.
Essential PTA education:
- Inspect the feet daily, including the soles, using a mirror or a caregiver if needed.
- Check inside shoes for foreign objects before wearing; never go barefoot.
- Wear well-fitting, protective footwear and seamless socks.
- Avoid extreme heat (hot water, heating pads) on insensate skin.
- Report any new redness, blister, callus, or skin breakdown promptly.
Balance and gait training also matter, because impaired sensation increases fall risk.
A PTA is collecting data on a patient with new lower-extremity weakness. The patient shows increased muscle tone, brisk knee and ankle reflexes, ankle clonus, and an upgoing great toe with plantar stimulation. These findings are MOST consistent with which type of lesion?
A PTA is providing home-program education to a patient with diabetic peripheral neuropathy who has reduced sensation in both feet. Which instruction is the HIGHEST priority for preventing serious complications?