High-Yield Neurology Topics for USMLE Step 1

Neurology is a behemoth of Step 1 studying. The amount of material is perhaps greater than in any other body system! After all, it does encompass a four-year residency while the broad strokes of internal medicine only necessitate three. My usual caveat to all high-yield reviews is especially true here in neurology. Trying to condense this enormous quantity of material into a few simple high-yield topics is as impossible as understanding Wernicke’s word salad.

The approach to neurology study for Step 1 will work just as it does in other sections. Build a strong foundation in normal anatomy and physiology of the system, and build on top of that framework with the pathology. Neuroanatomy is extremely important. So much of the practice of neurology is “localizing the lesion” based on a patient’s neurological deficits. This practice would be impossible without having a very firm handle on the anatomic layout of the brain, brain stem, spinal cord, and peripheral nervous system. Though it might be tricky to hold back, only tackle pathology when you get knowledge of neuroanatomy to a sufficient level of understanding.

Remember, what you see before you is just a place to start. It will point you in a particular direction to get the highest number of correct answers with putting in the least amount of work…pure efficiency. But don’t even think about stopping here. The more work you put in, the better your study plan, and most importantly, the more Qbank questions you answer, the better your chance of passing Step 1 will be. It’s really that simple.

Dopamine Pathways (6.5)

Dopamine…the chemical that floods our nervous systems every time we get a question right on Tutor Mode, and that green check pops up. This neurotransmitter is involved in so many of the body’s functions, and to keep them straight, it certainly helps to remember the four different pathways that utilize it.

The aforementioned one is the mesolimbic, responsible for drug reward and addiction—it’s overactive in patients with schizophrenia. Positive symptoms of schizophrenia like hallucinations and delusions are targeted by dopamine antagonists here. Decreased activity of the mesocortical pathway creates negative symptoms of schizophrenia like apathy and anhedonia. The nigrostriatal pathway is connected to the substantia nigra, and therefore, decreased activity leads to Parkinsonism.

Lastly, the tuberoinfundibular pathway is the dopamine tract involving prolactin. Recall that dopamine is occasionally known as Prolactin inhibitory factor; decreased dopamine means increased prolactin, leading to sexual dysfunction and galactorrhea. Don’t forget you can treat a prolactinoma with dopamine agonists cabergoline or bromocriptine!

Homunculous & Layout of Cortex (8.5)

Neuroanatomy! Huge topic! Understanding the layout of the cerebral cortex, the blood supply to each region, and the almighty Homunculus will pay incredible dividends.

In the cortex, your most important zones are as follows:

The motor cortex in the frontal lobe, its neighbor just behind the central sulcus, the primary sensory strip in the parietal lobe; the visual cortex in the occipital lobe; and the entire language pathway from the comprehension center in Wernicke’s area of the temporal lobe, along the arcuate fasciculus, and ending in the motor center of Broca’s area in the frontal lobe.

The sensory and motor strips have fascinating distributions in terms of matching body parts to brain chunks. You don’t need to have the finer points of the homunculus down pat. Just know that the most medial part of the brain is responsible for lower extremities, arm and hand at the superolateral section, and face most lateral.

Cerebral Perfusion & Artery Zones (9)

So many questions about the brain revolve around blood flow. There’s not a ton of oxygen reserve in the brain, so when blood flow is compromised, it’s only a matter of time before areas become ischemic. This leads to a stroke, the third most common cause of death worldwide.

Probably most devastating is a compromise to the middle cerebral artery (MCA), as it supplies major regions of the cortex involved in speech and movement of the upper extremities. The anterior cerebral artery (ACA) supplies the cortical region responsible for lower extremities. An issue with posterior circulation, whether the posterior cerebral artery (PCA), or one of the cerebellar arteries, would be the one to affect the visual cortex.

Remember, a stroke in just the PCA causes homonymous hemianopia with macular sparing since the MCA provides dual supply!

Cranial Nerves & Reflexes (9)

Part of the bedrock of medical education, the cranial nerves aren’t going anywhere. As we continue to sing the praises of knowledge of neuroanatomy, knowledge of the cranial nerves, their locations, and their functions is absolutely essential. Esoteric knowledge of all the different nuclei of cranial nerves in the brainstem is probably a bit more than you need to know. But you should expect to see the classic reflexes (e.g., pupillary, corneal, gag, jaw jerk) on exam day.

Some lesser mentioned (non-bulbar) but important cranial nerve functions: Baroreceptors (in the aortic arch and carotid sinus) feed afferent signals to the brain via cranial nerve IX, and exert their efferent effects via cranial nerve X. The vagus is responsible for so much! Responsible for vasovagal reflexes, digestion, control of the vocal cords, and parasympathetic innervation of the heart, this nerve affects nearly every major body system.

Spinal Cord Anatomy & Lesions (10)

Find a picture you like that displays a cross-section of the spinal cord. Then stare at it and commit it to memory. Don’t be afraid to put a lot of time into this. Once you understand where these tracts lay in the spinal cord, where they cross over to the other side of the body, and where their synapses take place, you will be ready to take any spinal cord lesion or trauma, and figure out what sort of phenotype it would create. More importantly, you can take a patient with a particular set of symptoms, and perform the essential task of neurology, localizing the lesion.

Ischemic Stroke and Hemorrhage (9)

As a leading cause of death in the US, strokes are at the epicenter of neurology. Your two main categories are ischemic and hemorrhagic. As expected, ischemic is caused by lack of oxygen in an area of the brain and hemorrhagic is secondary to bleeding.

How does an area of the brain become ischemic? This can be due to an embolus that travels to a cerebral vessel, blocking blood flow; a thrombus forming from a longstanding atherosclerotic plaque; or a period of hypotension in an area without any oxygen reserve.

Because blood flow is blocked by a clot, thrombolytic therapy (with TPA) provides the best chance of recovery. However, that can be devastating in a hemorrhagic stroke, as bleeding + blood thinning = catastrophic bleeding. Therefore, your first step is a head CT without contrast to rule out a brain bleed. Hemorrhagic strokes can be treated surgically or medically with blood pressure control and overall patient optimization.

Aphasia (8)

The linguistic pathway is as important as it is simple (for Step 1 purposes). Two main centers of the brain, connected by an anterior-posterior cortical pathway, are responsible for allowing us to comprehend and create language.

In the temporal lobe, Wernicke’s area is responsible for language comprehension. Patients with lesions here can make and say words without issue, but the words that come out are nonsensical (Wernicke’s word salad).

The arcuate fasciculus connects Wernicke’s area to Broca’s area, a section of eloquent cortex in the frontal lobe. If there’s a lesion in the arcuate fasciulus, a patient won’t be able to repeat the exact phrase someone tells them. An injury in Broca’s area doesn’t affect comprehension, but makes it very difficult for patients to get any words out (broken broca). These regions are found on the left side of the brain, and in the distribution of the middle cerebral artery (MCA).

Headaches (8)

As painful as they are prevalent, headaches can be debilitating in the afflicted. Keeping them compartmentalized into their three main varieties is the way to go:

Tension headaches are your run-of-the-mill hatband distribution headaches. While their exact cause is elusive, they are related to muscular tension and stress, and usually respond to NSAIDs.

Migraines are a bit more debilitating than tension headaches, and usually cause a throbbing on one side of the head for around 24 hours. Often associated with other symptoms like photophobia, phonophobia, and nausea, they can respond to triptans for abortive therapy. If they occur often enough, prophylactic therapy might be indicated with beta-blockers, tricyclic antidepressants, or antiepileptic drugs.

Cluster headaches are the rarest of the three, usually described as an ice pick behind the eyes that lasts for around 15 minutes. Look for other symptoms like tearing of the eyes or drooping of the eyelid unilaterally. Like migraines, cluster headaches are treated with triptans, but can also respond to 100% oxygen. As with any condition, if there are red flags (e.g., focal neurologic deficit, protracted duration, worst headache of life), a CT scan should be performed to rule out a bleed, stroke, or mass effect.

Neurodegenerative Disorders (9)

This collection of diseases can wreak havoc on patients, as many have no great cure or management strategy. The most virulent is Creutzfeldt-Jakob disease, a rapidly progressive dementia with occasional myoclonus. Its claim to fame is being prion-driven.

Alzheimer’s is quite common, and is marked by amyloid deposition and tau-proteins.

Parkinson’s disease is marked by the classic mnemonic TRAP of tremor (resting), rigidity, akinesia/bradykinesia, and postural instability. The board loves this disease because of its eloquent anatomic tie-in. The dopaminergic neurons of the substantia nigra die off; therefore, we can treat the disease with dopamine analogues like levodopa.

Huntington’s disease, a trinucleotide repeat disease (biochem tie-in! Remember anticipation?), is caused by atrophy of the basal ganglia. Chorea, mood changes, and depression are the symptoms you’ll most likely see.

Multiple Sclerosis (9)

Some important things you must know about MS. It’s a CNS disease, meaning you will see it affecting the brain and spinal cord, not the peripheral nervous system. When localizing the lesion, it’s useful to be able to rule out an entire subset of diseases simply by knowing which half of the nervous system is affected.

The classic disease definition is multiple CNS lesions separated by time (separate presentations), and space (2+ distinct anatomical deficits). An MRI (brain or spinal cord) is necessary to visualize white matter lesions. Like most autoimmune diseases, flares are treated with IV steroids, and are kept at bay with immune therapies (e.g., interferon, glatiramer).

One of the most common anatomic sites to suffer is the eye, with acute onset of optic neuritis, diplopia, nystagmus, or bilateral internuclear ophthalmoplegia (INO).

Brain Tumors (7.5)

The ability to differentiate brain tumors is something you need for Step 1 success. Most commonly you will come across glioblastoma multiforme (GBM), meningioma, and pituitary adenoma.

GBM is the most aggressive, causing necrosis and hemorrhage as it eats away brain tissue. Very poor prognosis and usually affects both lobes of the brain.

A meningioma is much more “benign” in the sense that it’s not indiscriminately eating the brain. It can be quite pathologic, however, if it compresses brain structures. Usually for a well-circumscribed tumor occurring along the meninges and not in the brain parenchyma, surgery is often curative.

Pituitary adenomas are testable because of both their systemic and mass effects. By compressing its neighbor, the optic chiasm, this tumor causes bitemporal hemianopia. In test questions, patients often describe “trouble changing lanes on the highway,” as peripheral vision is lost. Systemically, these tumors are usually secreting prolactin, causing menstruation and libido abnormalities, galactorrhea, and gynecomastia. Treat with surgery or dopamine (prolactin inhibitory factor) agonists like bromocriptine or cabergoline.

Upper vs. Lower Motor Neurons (8.5)

It all comes back to localizing the lesion. Other than ALS, which affects both upper and lower motor neurons, disease processes should affect only one subset of motor neurons.

For lower motor neurons, think decrease… decreased tone, decreased muscle bulk, and decreased reflexes.

Think increase for upper motor neuron injuries. They cause spastic tone, hyperreflexia, and upgoing Babinski sign.