Answers to Quiz 124 · Sensory Abnormalities
A peripheral nerve is damaged by chronic compression. Which sensations go first, while the others are still felt?
Answer: Touch and pressure
Compression hits the large fibres, which carry touch and pressure; the thin fibres for pain and temperature keep conducting, so those modalities are preserved. Revise sensory lesions and sensory function tests
Anesthesia of both hands and both feet, with the trunk spared, points to:
Answer: A distal, symmetrical polyneuropathy
This is glove and stocking anesthesia: the longest and largest fibres suffer most, so the loss is worst at the far ends of the limbs and is present on both sides. Revise sensory lesions and sensory function tests
Sensory ataxia in a polyneuropathy is explained by damage to:
Answer: Large kinesthetic fibres carrying position and vibration
The big kinesthetic fibres are the ones most affected, and losing position and vibration sense removes the feedback that steadies stance and gait. Losing the pain fibres instead leads to trophic ulcers. Revise sensory lesions and sensory function tests
A herniated intervertebral disc compresses one sensory nerve root. What is the expected finding?
Answer: Segmental anesthesia that is incomplete, because roots overlap
The loss follows the segment whose root is squeezed, but neighbouring roots overlap into that skin, so no patch is left entirely without sensation. Revise sensory lesions and sensory function tests
In your book's scheme of cord syndromes, the tabetic syndrome is produced by a lesion of:
Answer: One posterior column
Your book reserves the bilateral dorsal column lesion for posterior column syndrome and draws tabetic syndrome on one side; either way, position and vibration sense are what is lost, and Romberg sign may appear. Revise sensory lesions and sensory function tests
Posterior column syndrome closely resembles a cortical sensory lesion. According to your book, which finding tells them apart?
Answer: Loss of vibration sense
Your book says the loss of vibration is the distinguishing feature. Impaired object recognition and a widened two-point threshold occur in both, so neither separates them. Revise sensory lesions and sensory function tests
A stab wound hemisects the cord on the right at the mid-thoracic level. Below the injury you expect:
Answer: Right-sided loss of vibration and position sense, left-sided loss of pain and temperature
Dorsal column fibres climb uncrossed, so fine touch, vibration and position go on the side of the cut; pain and temperature fibres have already crossed into the opposite anterolateral system, so they go on the other side. Revise sensory lesions and sensory function tests
In Brown-Séquard syndrome, the paresis and spasticity of muscles are found:
Answer: On the same side as the hemisection
The corticospinal tract in the cut half has already crossed higher up, so it serves the muscles of that same side; cutting it there weakens and stiffens that side of the body. Revise sensory lesions and sensory function tests
After complete transection of the spinal cord, a narrow band of hyperesthesia is usually found:
Answer: Just above the numb zone
All sensation is abolished below the level of the cut, and a thin strip of heightened sensitivity typically borders the upper edge of the anesthetic area. Revise sensory lesions and sensory function tests
A cavity forms around the central canal of the cervical cord. The resulting sensory picture is:
Answer: Pain and temperature lost, touch and position preserved
The cavity interrupts the crossing lateral spinothalamic fibres but leaves the dorsal columns alone, which is the classic dissociated sensory loss of syringomyelia. Revise sensory lesions and sensory function tests
A patient develops sudden spastic paralysis with loss of pain and temperature below the lesion, while position sense stays normal. The likely lesion is:
Answer: Occlusion of the anterior spinal artery
Infarction of the ventral half of the cord takes out the spinothalamic and corticospinal tracts while sparing the dorsal columns, hence the preserved proprioception. Revise sensory lesions and sensory function tests
A one-sided lesion in the medulla produces loss of pain and temperature over:
Answer: One side of the face and the other side of the body
At that level the descending trigeminal tract has not yet crossed while the lateral spinothalamic tract already has, so the face and the body deficits land on opposite sides: crossed sensory loss. Revise sensory lesions and sensory function tests
Thalamic syndrome, in which a mildly painful stimulus provokes an exaggerated response and touch feels unpleasant, follows a lesion of which thalamic nuclei?
Answer: Lateral and ventral
Your book places thalamic syndrome in lesions of the lateral and ventral nuclei, with the pain threshold raised yet the response to pain exaggerated on the far side of the body. Revise sensory lesions and sensory function tests
Which of these is NOT counted among the cortical sensations?
Answer: Vibration sense
The cortex handles the spatial and discriminative side of sensation, so localization, two-point discrimination and stereognosis are the cortical sensations. Vibration is also impaired by a cortical lesion, but it is not one of the three. Revise sensory lesions and sensory function tests
Somatosensory evoked potentials are of greatest value in deciding:
Answer: Whether a conduction defect is peripheral or central
They test conduction in the large-diameter fibres all the way from peripheral nerve through brainstem and thalamus to cortex, so they separate a peripheral from a central lesion. Revise sensory lesions and sensory function tests
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