HY USMLE Q – Neuro

[00:00:00]How's it going guys? We have a 33-year-old woman with a 2-day history of worsening visual acuity in her left eye. It's 20/300.

[00:00:07]The right eye is normal. Babinski sign, upper motor neuron finding is seen bilaterally. BMI is 35.

[00:00:13]What's the most likely diagnosis? Choice A, ALS is wrong. So, ALS is the answer in USMLE when you have two things in a vignette. The first is you have a combo of upper motor neuron and lower motor neuron findings.

[00:00:27]Upper motor neuron findings like Babinski sign, clonus, hyperreflexia, hypertonia.

[00:00:36]Lower motor neuron findings, fasciculations, atrophy, weakness, hypotonia, hyporeflexia. So, you see a combination of UMN and LMN findings.

[00:00:46]That's the first thing. The second thing is no sensory abnormalities.

[00:00:51]Very easy for ALS. Give you a 12-line paragraph, you're not sure what's going on.

[00:00:56]They tell you that there's something wrong with a There's a sensory finding.

[00:01:00]You're like, boom, not ALS.

[00:01:03]Wrong [ __ ] answer.

[00:01:07]Choice B, and this is just degeneration of motor neurons mechanistically. Choice B, Charcot-Marie-Tooth disease, wrong.

[00:01:13]So, I've seen it show up once in history on a neuro form for TC K level stuff, but by all means, things can show up on Step 1.

[00:01:22]This is an idiopathic degeneration of neurons, and it will be the answer in USMLE if they mention the patient has pes cavus, so high-arched feet, and hammer toes, curled-in toes.

[00:01:36]I know it sounds weird, okay? You get miscellaneous neurologic deficits, but they'll and you're like, I have no idea what's going on, but then they literally say in the question, "Hammer toes and high-arched feet."

[00:01:48]And it's just Charcot-Marie-Tooth disease. Wrong [ __ ] answer.

[00:01:59]>> Choice C, CIDP, wrong [ __ ] answer.

[00:02:03]This is the answer on USMLE. Shows up once, okay?

[00:02:06]This is the answer on USMLE when the vignette sounds exactly like Guillain-Barré with ascending paralysis, but it's been going on for greater than 8 weeks. 8 weeks is technically the minimum cutoff. They might give you a situation where it's like 4 months and it's there's been gradually worsening ascending paralysis. You're like, "Hmm, that sounds like Guillain-Barré."

[00:02:29]But it's CIDP. Now, Guillain-Barré is also known as acute inflammatory demyelinating polyneuropathy.

[00:02:36]They don't have to mention triggers like dude went to a barbecue and there was bloody stool and it's Campylobacter.

[00:02:43]They don't do that. That's usually that's maybe like one out of four questions, one out of five questions.

[00:02:48]They'll just give you 24-year-old dude has ascending paralysis for the past 2 weeks and that's Guillain-Barré.

[00:02:55]Okay? Or they'll give it to you 4 months and that's CIDP, but technically at least 8 weeks is the cutoff and we call it CIDP. Shows up once, wrong [ __ ] answer.

[00:03:08]Choice D, Devic syndrome, wrong [ __ ] answer. This will be the answer on USMLE when it sounds exactly like multiple sclerosis, but they explicate that CSF IgG oligoclonal bands are negative.

[00:03:23]And then the answer will be antibodies against aquaporin 4.

[00:03:27]It shows up on a 2CK neuro form. It's if it's the first time you're hearing it, sounds very [ __ ] weird, I agree with you. If you've gone through my content, you'll know I've mentioned Devic syndrome.

[00:03:36]Okay? So, it's just an autoimmune condition that sounds like a mess.

[00:03:40]But the CSF IgG oligoclonal bands are negative. You're like, "Well, we don't mention here." Doesn't [ __ ] matter, okay? So, if we don't mention them, mention the finding at all, that's different from that it's actually negative.

[00:03:54]So, our correct answer is MS. Woman 20s to 30s who has optic neuritis, that's any problem with the eye.

[00:04:03]Decreased visual acuity, they can say diminished color vision, central scotoma, which is a blind spot.

[00:04:09]They like giving you Babinski sign, just a standard upper motor neuron finding.

[00:04:14]They can give you urge incontinence, very high yield. So, MS is when you've got white matter plaques in the CNS, brain and spinal cord. You have a T-cell attack against oligodendrocytes {slash} myelin basic protein. You need to know both of those.

[00:04:31]Oligodendrocytes, myelin basic protein, a T-cell attack. That's the pathophysiology for MS. You'd be amazed at the number of students that have asked, "What's the cause of MS? What's the pathophiz?" And they're not able to tell me that. Okay? So, we have optic neuritis here. You can also get internuclear ophthalmoplegia, aka medial longitudinal fasciculus syndrome.

[00:04:54]That's the whole fancy scenario of when you abduct with, let's say, your right eye, and then your left eye cannot adduct.

[00:05:07]And you would have MLF syndrome on the left. The side that cannot adduct is the side that's [ __ ] up.

[00:05:13]Okay? So, when you look to one side, when you abduct, you have to activate cranial nerve six, abducens nerve, but that has to sync with the contralateral oculomotor, cranial nerve three, in order to adduct the eye. That's called the MLF in the midbrain.

[00:05:29]Okay? So, just remember, if you get a situation and you're like, "Ooh, I'm iffy on all the neuroanatomy stuff. I suck at neuro, fine."

[00:05:37]You get a situation where they say, like, "She looks to the right and the left eye can't look to the right, also.

[00:05:49]And it There's a bit of nystagmus of the left eye. You say, "Well, that's MLF on the left cuz that's the side that's [ __ ] up, the side that cannot adduct."

[00:06:01]Multiple sclerosis.

[00:06:03]Correct answer.