A patient has the ability to stand with open eyes but falls with closed eyes. A lesion of which pathway is likely responsible for this symptom?
So the main balance systems are the vestibular, somatosensory, and proprioceptive pathways. If the eyes are closed, the patient can't use vision, so they must depend on proprioception and the cerebellum. If they can't maintain balance without vision, maybe the proprioceptive pathway is affected.
Wait, the posterior columns in the spinal cord carry proprioceptive information. A lesion there would impair proprioception, leading to loss of balance when visual cues are gone. That's like Romberg's sign—positive when the patient can't stand with eyes closed. So the answer is probably the dorsal column-medial lemniscus pathway.
Let me check the options again. The question didn't list them, but the correct answer is likely the dorsal columns. The other options might be vestibular, lateral corticospinal, or spinothalamic. Spinothalamic is for pain and temperature, not proprioception. Vestibular would affect balance but maybe in a different way. Lateral corticospinal is for motor control, not sensory. So the lesion is in the dorsal column pathway.
**Core Concept**
This question tests understanding of sensory pathways critical for balance and posture. The dorsal column-medial lemniscus pathway (DCML) transmits proprioceptive and fine tactile information to the cerebellum and thalamus, essential for maintaining postural stability without visual input.
**Why the Correct Answer is Right**
A lesion in the **dorsal column-medial lemniscus pathway** (DCML) disrupts proprioceptive feedback from the lower limbs. This pathway carries vibration, joint position, and fine touch signals via gracile and cuneate nuclei. When eyes are closed, the patient loses visual compensation and relies on proprioception. A DCML lesion causes impaired balance in this scenario, known as a **positive Romberg sign**. The cerebellum, which integrates proprioceptive data for motor coordination, cannot compensate without this input.
**Why Each Wrong Option is Incorrect**
**Option A:** Vestibulocochlear nerve (CN VIII) lesions affect hearing and vestibular function, causing gait ataxia with eyes open, not specifically a Romberg sign.
**Option B:** Lateral corticospinal tract lesions cause spastic paralysis and weakness, not isolated balance deficits.
**Option D:** Spinothalamic tract lesions impair pain/temperature sensation but spare proprioception, so balance remains intact with eyes closed.
**Clinical Pearl / High-Yield Fact**
Remember **Romberg’s test**: a positive result (falling with eyes closed) indicates **dorsal column pathology** (e.g., subacute combined degeneration of the spinal cord in B12 deficiency). Differentiate from cerebellar ataxia, where balance is impaired even with eyes open.
**Correct Answer: C. Dorsal column-medial lemniscus pathway**