## **Core Concept**
The question tests knowledge of neurological disorders affecting reflexes and plantar responses. Specifically, it focuses on the combination of bilateral loss of tendon jerk and extensor plantar response, which are indicative of upper motor neuron (UMN) and lower motor neuron (LMN) lesions or a condition affecting both.

## **Why the Correct Answer is Right**
The correct answer, **C. Tabes dorsalis**, is associated with a combination of UMN and LMN signs due to its pathophysiology. Tabes dorsalis is a form of neurosyphilis characterized by degeneration of the dorsal columns of the spinal cord and the roots. This degeneration leads to loss of deep tendon reflexes (LMN sign) and can also present with upper motor neuron signs, including extensor plantar responses, due to the involvement of the corticospinal tracts indirectly through the disease process.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because the condition described does not match the typical presentation of the disease associated with it.
- **Option B:** This option is incorrect as it does not align with the clinical presentation of bilateral loss of tendon jerk and extensor plantar response.
- **Option D:** This option is incorrect because it represents a condition that does not typically present with the combination of reflex and plantar response abnormalities described.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that tabes dorsalis, a complication of syphilis, classically presents with areflexia (loss of reflexes), ataxia, and sensory disturbances. The presence of bilateral extensor plantar responses in the context of areflexia is highly suggestive of a condition affecting both UMN and LMN pathways.

## **Correct Answer:** . **C. Tabes dorsalis**