USMLE® Step 1 style questions USMLE
USMLE® Step 2 style questions USMLE
A 30-year-old woman comes to the clinic because of bilateral flaccid paralysis of the upper extremities. On physical examination, she has flaccid paralysis in both of her arms, as well as a loss of pain and temperature sensation in both arms. She also has a headache and neck pain exacerbated by cough and valsalva maneuver. She has no other identifiable symptoms other than headaches during exercise. Which of the following is her likely diagnosis?
In syringomyelia, syrinx means cyst or cavity, and myelia means a condition of the spinal cord.
So, syringomyelia is a cystic enlargement of the spinal cord, and it typically starts medially and enlarges outwards, eventually damaging the spinothalamic tract, which is a part of the spinal cord that sends sensory signals about pain, pressure, temperature, and touch to the brain.
Now, the spinal cord itself is composed of both grey and white matter.
Grey matter is found within medial portion of the spinal cord and is shaped like a butterfly. This is where the cell bodies of different neurons can be found.
In the center of the grey matter there’s a small cavity the central canal which is filled with cerebrospinal fluid.
Cerebrospinal fluid helps provide nutrients and mechanical support to the brain and spinal cord.
Surrounding the grey matter is white matter, which consists of the axons of various neurons.
The spinal cord has different neural tracts that carry sensory information to and from the brain.
The corticospinal tract is a descending pathway which carries motor information from the brain to various muscles.
The dorsal column, located in the posterior portion of the spinal cord, is responsible for sensing pressure, vibration, fine touch, and proprioception, or the awareness of one’s body position in space.
Then there’s the spinothalamic tract, which is divided into two distinct tracts - the lateral spinothalamic tract which is responsible for sensing pain, pressure, and temperature, as well as the anterior spinothalamic tract which senses crude touch.
The spinothalamic tract carries all of this sensory information from the spine up to the thalamus of the brain where the information is processed.
This happens through three neurons that synapse with one another.
First, a primary neuron carries sensory information, such as pain, from the skin to the dorsal horn of the spinal cord, where it synapses with a secondary neuron.
The secondary neuron ascends 1-2 vertebral levels and decussates or crosses to the opposite side of the spinal cord via an area of white matter called the anterior white commissure.
The secondary neuron then ascends up the length of the spinal cord via the anterior or lateral spinothalamic tracts, eventually synapsing at the ventral posterior nuclei of the thalamus.
Finally, from there, a third neuron arises from nuclei in the thalamus and carries the signal to the primary sensory cortex or the postcentral gyrus of the brain where the sensory signal is interpreted.
In syringomyelia, the central canal of the spinal cord that houses the cerebrospinal fluid gradually expands.
In this condition the cerebellar and brainstem tissue slip down into the foramen magnum—the opening at the base of the skull.
This malformation results in a variety of balance and movement symptoms related to the cerebellum and usually results in hydrocephalus—an abnormal accumulation of cerebrospinal fluid in the brain.
Normally cerebrospinal fluid would flow through the four ventricles of the brain, and after the 4th ventricle, the fluid would have two options.
It could exit the ventricular system through openings called the medial and lateral apertures and into the subarachnoid space where it’s reabsorbed.