**Core Concept**
Hypotonia refers to decreased muscle tone, resulting in weak or floppy muscles. Brisk tendon reflexes, on the other hand, indicate an increased neural excitability. This combination is often seen in conditions affecting the upper motor neuron (UMN) pathways, which control voluntary muscle movement.

**Why the Correct Answer is Right**
The correct answer is associated with a condition that affects the corticospinal tract, a critical UMN pathway. Damage to this tract can lead to a loss of inhibitory control over motor neurons, resulting in increased excitability and brisk tendon reflexes. Simultaneously, the decreased muscle tone (hypotonia) is due to the loss of corticospinal input to the muscle spindles, which are responsible for regulating muscle tone.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not typically present with hypotonia. Conditions affecting the peripheral nervous system or muscle itself, such as peripheral neuropathy or myopathy, may result in weakness and decreased reflexes.
* **Option B:** This option is incorrect because it is associated with increased muscle tone, not hypotonia. Conditions like Parkinson's disease or dystonia present with hypertonia and decreased reflexes.
* **Option C:** This option is incorrect because it primarily affects the peripheral nervous system. Conditions like Guillain-Barré syndrome present with areflexia (absence of reflexes) and decreased muscle tone.

**Clinical Pearl / High-Yield Fact**
Remember the phrase "UMN lesions = decreased tone, brisk reflexes" to help differentiate conditions affecting the upper motor neuron pathways from those affecting the peripheral nervous system or muscle.

**Correct Answer: C. Spinal cord injury**