Neuro q

[shigella123]

A 80 year old man was observed to have an episode of loss of consciousness. Upon awakening he complained of double vision and there was a notable tremor in his left arm. There was a mildly elevated blood pressure. Mental status was good and speech was articulate and appropriate. With the eyelids retracted the right eye had a dilated pupil and a lateral strabismus. On attempted lateral gaze to the left the right eye would not proceed across the midline. The right pupil did not constrict in either the direct or consensual pupillary light reflexes. Hearing was normal as were cranial nerves 5 through 12. Pain and temperature sensation from the face and body was normal bilaterally. Proprioception and vibratory sense on the right side of the body was normal but was diminished on the left. Muscle strength on the left was slightly diminished and deep tendon reflexes were slightly increased. There was no Babinski sign. The finger-to-nose test was normal on the right but the left arm showed an intention tremor and dysmetria. There were occasional involuntary movements of the left arm. What is the most likely diagnosis?

A) Dorsal midbrain syndrome
B) Paramedian midbrain syndrome
C) Lateral medullary syndrome
D) Medial medullary syndrome
E) Facial colliculus syndrome
F) Medial longitudinal syndrome

Show your thought process please.

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[thehundredthone]

The loss of consciousness tells you this is probably posterior circulation. The absence of a direct and consensual light reflex tells you that CN III is affected, telling you that the lesion is at the level of the midbrain or above. Vibratory and proprioception deficit tells you that the dorsal column is affected, which at the level of the brainstem has become the medial lemniscus. The corticospinal and spinothalamic tracts are also involved, to some extent. Hence the lesion in is the medial midbrain, i.e. the paramedian midbrain or Benedikt syndrome.

Dorsal midbrain lesions would not involve the medial lemniscus. Medullary lesions would not involve the oculumotor nerve. Facial colliculus lesions would involve, well, the facial nerve. Medial longitudinal lesions would only affect the gaze.

 

[surgok]

superior cerebellar decussation explains the hemiataxia.

 

[shigella123]

Thank you.

I thought medial midbrain syndrome was called Weber syndrome which included the CN 3+PCA+CBT+CST.

 

[1dayatatime]

Omg where is this q from and why is it so long!

 

[thehundredthone]

Thank you.

I thought medial midbrain syndrome was called Weber syndrome which included the CN 3+PCA+CBT+CST.

You're right, that is Weber's syndrome. But in this case the CST is hardly affected, and there is definitely no CBT involvement. It's more of a ventro-medial lesion. Benedikt's syndrome is paramedian, involving the tegmentum area, and thus hits the cerebellar decussation causing ataxia. I guess I forgot to mention one of the main clinching features of the syndrome. I apologize.

Useless factoid: Nothnagel's syndrome arises from a lesion of the tectum rather than the tegmentum and presents with uni or bilateral CN III palsy and ipsilateral hemiataxia. It is usually caused by a tumour like a glioma.

 

[shigella123]

Omg where is this q from and why is it so long!

I really wish all the questions on uworld were this long so we could get better practice on them instead of learning to deal with them on the exam day. I found this q while searching for something else and decided to share it with you guys.

 

[thehundredthone]

Neurology questions can be long because they are trying to give you an idea about what is and isn't involved. That is how you would localize the lesion.

On my Step 1 there weren't as many long questions as I had expected. Step 2 was where they all turned up.