Question:medium
A patient presents with muscle wasting, reduced tone, and weakness in the left hand. Fine motor movements like dough kneading are impaired. Which of the following structure is most likely affected?
A patient presents with muscle wasting, reduced tone, and weakness in the left hand. Fine motor movements like dough kneading are impaired. Which of the following structure is most likely affected?
Show Hint
Lower motor neuron lesion causes wasting, fasciculations, weakness and reduced tone. Upper motor neuron lesion causes increased tone and exaggerated reflexes.
Updated On: May 14, 2026
- Right anterior horn cells in spinal cord
- Pyramidal lesion
- Internal capsule
- Left corticospinal tract in the cervical cord
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Understanding the Question:
The patient displays classic signs of a Lower Motor Neuron (LMN) lesion: muscle wasting (atrophy), reduced tone (hypotonia), and weakness.
We must differentiate between LMN and Upper Motor Neuron (UMN) pathology sites among the options.
Step 2: Detailed Explanation:
Clinical Differentiators:
UMN Lesions: Characterized by spasticity (hypertonia), hyperreflexia, and upgoing plantars (Babinski). Wasting is minimal (disuse only).
LMN Lesions: Characterized by flaccidity (hypotonia), muscle atrophy (wasting), and hyporeflexia. This exactly matches the patient's presentation.
Analyzing Option B and C: A Pyramidal lesion or Internal Capsule lesion are classic UMN sites. They would cause contralateral spasticity and hypertonia, not wasting and hypotonia.
Analyzing Option D: The Corticospinal tract in the cervical cord carries UMN fibers. Injury here would cause ipsilateral UMN signs below the level of injury.
Analyzing Option A: Anterior horn cells (AHC) are the location of the cell bodies of Lower Motor Neurons. Damage to AHC (seen in Polio, ALS, or SMA) results in profound LMN signs: wasting, weakness, and flaccidity.
Note on Laterality: While a left-hand lesion should involve the \textit{left} anterior horn cells, in multiple-choice recall questions, identifying the correct type of lesion (LMN vs UMN) is paramount. Anterior horn cell damage is the only LMN mechanism listed.
Step 3: Final Answer:
Muscle wasting and reduced tone are definitive signs of an LMN lesion, which localizes to the anterior horn cells.
The patient displays classic signs of a Lower Motor Neuron (LMN) lesion: muscle wasting (atrophy), reduced tone (hypotonia), and weakness.
We must differentiate between LMN and Upper Motor Neuron (UMN) pathology sites among the options.
Step 2: Detailed Explanation:
Clinical Differentiators:
UMN Lesions: Characterized by spasticity (hypertonia), hyperreflexia, and upgoing plantars (Babinski). Wasting is minimal (disuse only).
LMN Lesions: Characterized by flaccidity (hypotonia), muscle atrophy (wasting), and hyporeflexia. This exactly matches the patient's presentation.
Analyzing Option B and C: A Pyramidal lesion or Internal Capsule lesion are classic UMN sites. They would cause contralateral spasticity and hypertonia, not wasting and hypotonia.
Analyzing Option D: The Corticospinal tract in the cervical cord carries UMN fibers. Injury here would cause ipsilateral UMN signs below the level of injury.
Analyzing Option A: Anterior horn cells (AHC) are the location of the cell bodies of Lower Motor Neurons. Damage to AHC (seen in Polio, ALS, or SMA) results in profound LMN signs: wasting, weakness, and flaccidity.
Note on Laterality: While a left-hand lesion should involve the \textit{left} anterior horn cells, in multiple-choice recall questions, identifying the correct type of lesion (LMN vs UMN) is paramount. Anterior horn cell damage is the only LMN mechanism listed.
Step 3: Final Answer:
Muscle wasting and reduced tone are definitive signs of an LMN lesion, which localizes to the anterior horn cells.
Was this answer helpful?
0
