A 23-year-old woman comes to the physician because of an 8-month history of weakness and intermittent burning pain in her neck, shoulders, and arms. She was involved in a motor vehicle collision 1 year ago. Examination of the upper extremities shows absent reflexes, muscle weakness, and fasciculations bilaterally. Sensation to temperature and pain is absent; vibration and proprioception are preserved. The pupils are equal and reactive to light. Which of the following is the most likely diagnosis?
Q52
A 47-year-old man comes to the emergency department because of urinary and fecal incontinence for 6 hours. Earlier in the day, he suffered a fall at a construction site and sustained injuries to his back and thighs but did not seek medical attention. He took ibuprofen for lower back pain. His temperature is 36.9°C (98.4°F), pulse is 80/min, and blood pressure is 132/84 mm Hg. Examination shows tenderness over the lumbar spine, bilateral lower extremity weakness, absent ankle jerk reflexes, and preserved patellar reflexes. There is decreased rectal tone. An ultrasound of the bladder shows a full bladder. Which of the following is the most likely diagnosis?
Q53
You are called to see a chemotherapy patient who is complaining of severe nausea. This patient is a 52-year-old male with acute lymphoblastic leukemia (ALL) who began his first cycle of chemotherapy 2 days ago. Which of the following structures is involved in the pathway responsible for this patient's nausea?
Q54
A 58-year-old woman presents to her primary care doctor with her husband. The patient's husband reports that his wife has been acting "funny" ever since she was in a motor vehicle accident 2 months ago. She's been very rude to him, their children, and her friends, often saying inappropriate things. She is not interested in her previous hobbies and will not watch her favorite television shows or play cards. Which of the following regions is suspicious for injury?
Q55
A 65-year-old woman presents to her physician with the complaint of ringing in her right ear. She says it started about 3 months ago with associated progressive difficulty in hearing on the same side. Past medical history is significant for a hysterectomy 5 years ago due to dysfunctional uterine bleeding. She is currently not taking any medications. She is a non-smoker and drinks socially. On otoscopic examination, a red-blue pulsatile mass is observed behind the right tympanic membrane. A noncontrast CT scan of the head shows significant bone destruction resulting in a larger jugular foramen highly suggestive of a tumor derived from neural crest cells. Which of the cranial nerves are most likely to be involved in this type of lesion?
Q56
A 68-year-old man is brought to the emergency department by ambulance after he was found to be altered at home. Specifically, his wife says that he fell and was unable to get back up while walking to bed. When she approached him, she found that he was unable to move his left leg. His past medical history is significant for hypertension, atrial fibrillation, and diabetes. In addition, he has a 20-pack-year smoking history. On presentation, he is found to still have difficulty moving his left leg though motor function in his left arm is completely intact. The cause of this patient's symptoms most likely occurred in an artery supplying which of the following brain regions?
Q57
A 42-year-old woman presents with loss of sensation in her left arm and hand. A rapid evaluation is performed to rule out stroke. No other focal neurologic deficits are found except for a loss of fine touch sensation in a C6 dermatome pattern. Further evaluation reveals that the patient was recently sick with an upper respiratory infection. A biopsy is performed and shows destruction of the cell bodies of sensory nerves. Which of the following structures has most likely been damaged?
Q58
A 27-year-old woman comes to the clinic for blisters on both hands. The patient has a past medical history of asthma, eczema, and a car accident 2 years ago where she sustained a concussion. She also reports frequent transient episodes of blurred vision that clear with artificial tears. When asked about her blisters, the patient claims she was baking yesterday and forgot to take the pan out with oven gloves. Physical examination demonstrates weeping blisters bilaterally concentrated along the palmar surfaces of both hands and decreased pinprick sensation along the arms bilaterally. What is the most likely explanation of this patient’s symptoms?
Q59
A 60-year-old man comes to the physician because his wife has noticed that his left eye looks smaller than his right. He has had worsening left shoulder and arm pain for 3 months. He has smoked two packs of cigarettes daily for 35 years. Examination shows left-sided ptosis. The pupils are unequal but reactive to light; when measured in dim light, the left pupil is 3 mm and the right pupil is 5 mm. Which of the following is the most likely cause of this patient's ophthalmologic symptoms?
Q60
A 60-year-old African American woman presents to her ophthalmologist with blurry vision. She reports a 2-month history of decreased vision primarily affecting her right eye. Her past medical history is notable for type 1 diabetes and hypertension. She takes insulin and enalapril. She has a 40-pack-year smoking history and drinks a glass of wine at dinner each night. Her family history is notable for glaucoma in her mother and severe diabetes complicated by nephropathy and retinopathy in her father. Her temperature is 99°F (37.2°C), blood pressure is 134/82 mmHg, pulse is 88/min, and respirations are 18/min. On exam, she is well-appearing and in no acute distress. The physician asks the patient to look forward and shines a penlight first in one eye, then the other, alternating quickly to observe the pupillary response to the light. When the light is shined in the right eye, both pupils partially constrict. When the light is shined in the left eye, both pupils constrict further. When the light is moved back to the right eye, both eyes dilate slightly to a partially constricted state. Where is the most likely site of this patient’s lesion?
Neuroanatomy US Medical PG Practice Questions and MCQs
Question 51: A 23-year-old woman comes to the physician because of an 8-month history of weakness and intermittent burning pain in her neck, shoulders, and arms. She was involved in a motor vehicle collision 1 year ago. Examination of the upper extremities shows absent reflexes, muscle weakness, and fasciculations bilaterally. Sensation to temperature and pain is absent; vibration and proprioception are preserved. The pupils are equal and reactive to light. Which of the following is the most likely diagnosis?
A. Subacute combined degeneration
B. Cervical disk prolapse
C. Amytrophic lateral sclerosis
D. Syringomyelia (Correct Answer)
E. Tabes dorsalis
Explanation: ***Syringomyelia***
- The combination of **absent reflexes**, **muscle weakness**, and **fasciculations** (lower motor neuron signs) along with **loss of temperature and pain sensation** (spinothalamic tract) and preserved vibration/proprioception (dorsal columns) in the upper extremities is highly characteristic of syringomyelia.
- The history of a **motor vehicle collision** a year prior suggests a potential trauma-induced cause of the syrinx, which can develop months to years after the initial injury.
*Subacute combined degeneration*
- This condition is caused by **Vitamin B12 deficiency** and typically presents with demyelination of the dorsal columns and lateral corticospinal tracts.
- It would manifest as **impaired vibration and proprioception** (dorsal column signs) and spasticity, rather than the dissociated sensory loss and lower motor neuron signs seen here.
*Cervical disk prolapse*
- While it can cause neck pain and weakness, cervical disk prolapse usually results in **radicular symptoms** affecting a specific dermatome and myotome, and often involves compressive myelopathy if severe.
- It typically does not cause the widespread, bilateral lower motor neuron signs and the specific dissociated sensory loss pattern (loss of pain/temperature with preserved vibration/proprioception) observed in this patient.
*Amytrophic lateral sclerosis*
- ALS presents with a combination of **upper and lower motor neuron signs**, including weakness, fasciculations, and spasticity.
- However, **sensory function is typically spared** in ALS, which contradicts the patient's prominent loss of pain and temperature sensation.
*Tabes dorsalis*
- This is a late manifestation of **syphilis** affecting the dorsal columns, leading to a loss of **vibration and proprioception**, as well as Argyll Robertson pupils.
- The patient's preserved vibration and proprioception, coupled with lost pain/temperature sensation and lower motor neuron signs, rule out tabes dorsalis.
Question 52: A 47-year-old man comes to the emergency department because of urinary and fecal incontinence for 6 hours. Earlier in the day, he suffered a fall at a construction site and sustained injuries to his back and thighs but did not seek medical attention. He took ibuprofen for lower back pain. His temperature is 36.9°C (98.4°F), pulse is 80/min, and blood pressure is 132/84 mm Hg. Examination shows tenderness over the lumbar spine, bilateral lower extremity weakness, absent ankle jerk reflexes, and preserved patellar reflexes. There is decreased rectal tone. An ultrasound of the bladder shows a full bladder. Which of the following is the most likely diagnosis?
A. Cerebellar stroke
B. Spinal epidural abscess
C. Anterior spinal cord syndrome
D. Conus medullaris syndrome (Correct Answer)
E. Brown-Sequard syndrome
Explanation: ***Conus medullaris syndrome***
- The combination of **bilateral lower extremity weakness**, **urinary and fecal incontinence**, **decreased rectal tone**, and a **full bladder** is characteristic of conus medullaris syndrome. This syndrome results from damage to the **conus medullaris** (the terminal part of the spinal cord), which typically involves the **S3-S5 nerve roots**.
- **Absent ankle jerk reflexes** (S1-S2) with **preserved patellar reflexes** (L2-L4) further pinpoints the lesion to the lower lumbar/sacral spinal cord segments, consistent with conus medullaris involvement. The recent **fall with back injury** is a predisposing factor.
*Cerebellar stroke*
- **Cerebellar stroke** would primarily manifest with symptoms of **ataxia**, **dysarthria**, **nystagmus**, and **vertigo**, without direct involvement of bladder/bowel function or specific lower extremity reflex abnormalities as described.
- While a stroke can cause weakness, it would typically be **unilateral** or involve specific cortical patterns, and not generally present with this constellation of lower spinal cord signs.
*Spinal epidural abscess*
- A **spinal epidural abscess** would typically present with **fever**, **severe localized back pain**, and progressive **neurological deficits**, often following an infection or recent spinal procedure.
- While it can cause neurological deficits similar to the conus medullaris syndrome, the absence of **fever** and the acute onset following trauma makes an abscess less likely in this scenario.
*Anterior spinal cord syndrome*
- **Anterior spinal cord syndrome** primarily affects the **anterior two-thirds of the spinal cord**, leading to **motor paralysis** below the lesion and **loss of pain and temperature sensation**, while **proprioception** and **vibration sense are preserved**.
- Although it can cause motor weakness and bladder dysfunction, the isolated loss of ankle jerk reflexes with preserved patellar reflexes and the specific pattern of incontinence are more indicative of conus medullaris involvement.
*Brown-Sequard syndrome*
- **Brown-Séquard syndrome** is characterized by **ipsilateral motor paralysis** and loss of **proprioception/vibration sensation**, along with **contralateral loss of pain and temperature sensation** below the level of the lesion, due to hemisection of the spinal cord.
- This patient presents with **bilateral weakness** and specific bladder/bowel dysfunction, which is inconsistent with the typical lateralized deficits seen in Brown-Séquard syndrome.
Question 53: You are called to see a chemotherapy patient who is complaining of severe nausea. This patient is a 52-year-old male with acute lymphoblastic leukemia (ALL) who began his first cycle of chemotherapy 2 days ago. Which of the following structures is involved in the pathway responsible for this patient's nausea?
A. Lateral geniculate nucleus
B. Posterior hypothalamus
C. Ventral posterolateral nucleus
D. Medulla oblongata (Correct Answer)
E. Medial geniculate nucleus
Explanation: ***Medulla oblongata***
- The **chemoreceptor trigger zone (CTZ)**, located in the **area postrema** of the **medulla oblongata**, is highly permeable and detects **blood-borne toxins**, such as chemotherapy agents.
- Upon activation, the CTZ sends signals to the **vomiting center** (also in the medulla), initiating the nausea and vomiting reflex.
*Lateral geniculate nucleus*
- This nucleus is part of the **thalamus** and is primarily involved in relaying **visual information** from the retina to the primary visual cortex.
- It plays no direct role in the pathways mediating chemotherapy-induced nausea and vomiting.
*Posterior hypothalamus*
- The posterior hypothalamus is involved in various autonomic functions including **arousal**, **sleep-wake cycles**, and **thermoregulation**.
- While it has broad autonomic control, it is not a direct or primary center for processing emetic stimuli.
*Ventral posterolateral nucleus*
- This thalamic nucleus is crucial for relaying **sensory information** (pain, temperature, touch, proprioception) from the body to the primary somatosensory cortex.
- It has no direct involvement in the mechanism of chemotherapy-induced nausea.
*Medial geniculate nucleus*
- Located in the **thalamus**, this nucleus is a key relay station for **auditory information**, transmitting signals from the inferior colliculus to the primary auditory cortex.
- It is unrelated to the pathways responsible for nausea and vomiting.
Question 54: A 58-year-old woman presents to her primary care doctor with her husband. The patient's husband reports that his wife has been acting "funny" ever since she was in a motor vehicle accident 2 months ago. She's been very rude to him, their children, and her friends, often saying inappropriate things. She is not interested in her previous hobbies and will not watch her favorite television shows or play cards. Which of the following regions is suspicious for injury?
A. Occipital lobe
B. Frontal lobe (Correct Answer)
C. Temporal lobe
D. Motor cortex
E. Broca's area
Explanation: ***Frontal lobe***
- The frontal lobe governs **executive functions**, including **social behavior**, personality, judgment, and emotional regulation.
- Damage here often leads to **disinhibition**, personality changes, and loss of interest in previously enjoyed activities, consistent with the patient's rude behavior and apathy.
*Occipital lobe*
- The occipital lobe is primarily responsible for **visual processing**.
- Injury typically results in **visual field deficits** or visual agnosia, not behavioral changes.
*Temporal lobe*
- The temporal lobe is involved in **memory**, **hearing**, and language comprehension.
- While damage can cause memory issues or aphasia, it's less commonly associated with the prominent **executive dysfunction** and personality changes described.
*Motor cortex*
- The motor cortex controls **voluntary movements**.
- Damage would primarily manifest as **weakness** or paralysis, not changes in mood or social conduct.
*Broca's area*
- **Broca's area** is a specific region within the frontal lobe responsible for **speech production**.
- Damage would lead to **expressive (Broca's) aphasia**, characterized by difficulty forming words or sentences, rather than broad personality changes or social disinhibition.
Question 55: A 65-year-old woman presents to her physician with the complaint of ringing in her right ear. She says it started about 3 months ago with associated progressive difficulty in hearing on the same side. Past medical history is significant for a hysterectomy 5 years ago due to dysfunctional uterine bleeding. She is currently not taking any medications. She is a non-smoker and drinks socially. On otoscopic examination, a red-blue pulsatile mass is observed behind the right tympanic membrane. A noncontrast CT scan of the head shows significant bone destruction resulting in a larger jugular foramen highly suggestive of a tumor derived from neural crest cells. Which of the cranial nerves are most likely to be involved in this type of lesion?
A. Cranial nerves I, II, V
B. Cranial nerves III, IV, VI
C. Cranial nerves IX, X (Correct Answer)
D. Cranial nerves VII & VIII
E. Cranial nerves X, XI, XII
Explanation: ***Cranial nerves IX, X***
- The symptoms of **tinnitus** and **hearing loss**, along with a **pulsatile retrotympanic mass** and **jugular foramen bone destruction**, strongly suggest a **glomus jugulare tumor**. These tumors arise from **chemoreceptor cells (paraganglia)** derived from neural crest cells located in the jugular foramen.
- The **jugular foramen** transmits the **glossopharyngeal (IX), vagus (X)**, and **accessory (XI)** cranial nerves. However, **CN IX and X are the most commonly and earliest affected** by glomus jugulare tumors due to their anatomical position.
- **Clinical involvement** of CN IX and X leads to symptoms like **dysphagia**, **hoarseness**, **loss of gag reflex**, and **vagal nerve dysfunctions**. While CN XI also passes through the jugular foramen, its involvement is typically **later and less symptomatic** in the early stages of tumor growth.
*Cranial nerves I, II, V*
- **Cranial nerve I (olfactory)** and **II (optic)** are involved in smell and vision, respectively, and are not affected by lesions in the jugular foramen.
- **Cranial nerve V (trigeminal)** supplies sensation to the face and muscles of mastication; it exits through the superior orbital fissure and foramen rotundum/ovale, not the jugular foramen.
*Cranial nerves III, IV, VI*
- These nerves (**oculomotor, trochlear, abducens**) are responsible for eye movements and are located within the **cavernous sinus** and orbit.
- Involvement of these nerves is typically associated with lesions of the cavernous sinus or superior orbital fissure, not the jugular foramen.
*Cranial nerves VII & VIII*
- **Cranial nerve VII (facial)** and **VIII (vestibulocochlear)** pass through the **internal auditory canal**, not the jugular foramen.
- While acoustic neuromas (vestibular schwannomas) cause hearing loss and involve CN VIII, a **pulsatile mass** and **jugular foramen destruction** are not characteristic of this type of lesion.
*Cranial nerves X, XI, XII*
- While **cranial nerve X (vagus)** and **XI (accessory)** do pass through the jugular foramen, **cranial nerve XII (hypoglossal)** passes through the **hypoglossal canal**, which is a completely separate opening anterior and medial to the jugular foramen.
- This option is **anatomically incorrect** because CN XII is not associated with the jugular foramen. Furthermore, the **most clinically relevant** nerves affected early in glomus jugulare tumors are CN IX and X, making the first option more accurate for "most likely to be involved."
Question 56: A 68-year-old man is brought to the emergency department by ambulance after he was found to be altered at home. Specifically, his wife says that he fell and was unable to get back up while walking to bed. When she approached him, she found that he was unable to move his left leg. His past medical history is significant for hypertension, atrial fibrillation, and diabetes. In addition, he has a 20-pack-year smoking history. On presentation, he is found to still have difficulty moving his left leg though motor function in his left arm is completely intact. The cause of this patient's symptoms most likely occurred in an artery supplying which of the following brain regions?
A. Motor cortex (ACA) (Correct Answer)
B. Cerebellum (PICA/SCA)
C. Occipital cortex (PCA)
D. Brainstem (Vertebrobasilar)
E. Motor cortex (MCA)
Explanation: ***Motor cortex (ACA)***
- The patient's inability to move his **left leg** while his **left arm** remains intact points to an injury in the **right cerebral hemisphere** affecting the leg area of the motor cortex.
- The leg area of the **primary motor cortex** is primarily supplied by the **anterior cerebral artery (ACA)**, making an ACA stroke the most likely cause.
*Motor cortex (MCA)*
- The **middle cerebral artery (MCA)** primarily supplies the motor cortex areas responsible for the **face and arm**, not typically isolated leg weakness.
- If the MCA were affected, you would expect to see involvement of the face and/or arm on the contralateral side in addition to leg weakness.
*Brainstem (Vertebrobasilar)*
- A **brainstem stroke** would likely present with more widespread neurological deficits, including **cranial nerve palsies**, ataxia, or altered consciousness.
- Isolated contralateral leg weakness without arm involvement is not characteristic of a brainstem lesion.
*Cerebellum (PICA/SCA)*
- The **cerebellum** is primarily involved in **coordination and balance**, not direct motor strength.
- A cerebellar stroke would present with symptoms like **ataxia**, dysarthria, or nystagmus, not isolated paralysis.
*Occipital cortex (PCA)*
- The **occipital cortex** is primarily responsible for **vision**.
- A posterior cerebral artery (PCA) stroke would typically cause **visual field defects** (e.g., contralateral homonymous hemianopia) rather than motor weakness.
Question 57: A 42-year-old woman presents with loss of sensation in her left arm and hand. A rapid evaluation is performed to rule out stroke. No other focal neurologic deficits are found except for a loss of fine touch sensation in a C6 dermatome pattern. Further evaluation reveals that the patient was recently sick with an upper respiratory infection. A biopsy is performed and shows destruction of the cell bodies of sensory nerves. Which of the following structures has most likely been damaged?
A. Dorsal root ganglion (Correct Answer)
B. Meissner's corpuscles
C. Ventral horn
D. Dorsal column
E. Lateral corticospinal tract
Explanation: ***Dorsal root ganglion***
- The **dorsal root ganglia** contain the **cell bodies of sensory neurons**, including those responsible for fine touch. Damage to these cell bodies, as indicated by the biopsy finding of "destruction of the cell bodies of sensory nerves," would directly lead to the observed loss of sensation.
- The **C6 dermatome pattern** further localizes the damage to the cervical region of the spinal cord, consistent with the location of the C6 dorsal root ganglion.
*Meissner's corpuscles*
- **Meissner's corpuscles** are **mechanoreceptors** located in the skin that are responsible for detecting light touch and vibration, not the cell bodies of sensory nerves themselves.
- Damage to these corpuscles would affect sensation, but the pathology describes destruction of **cell bodies**, not the sensory endings.
*Ventral horn*
- The **ventral horn** of the spinal cord contains the **cell bodies of motor neurons** that innervate skeletal muscles.
- Damage to the ventral horn would primarily result in **motor deficits** (weakness, paralysis), not sensory loss.
*Dorsal column*
- The **dorsal column** tracts (gracile and cuneate fasciculi) are *white matter* pathways in the spinal cord that carry sensory information, including fine touch and proprioception, from the periphery to the brain.
- While damage to the dorsal column would cause sensory loss, the biopsy finding of destroyed "cell bodies of sensory nerves" points to a lesion *before* the axons enter the spinal cord, i.e., in the dorsal root ganglion.
*Lateral corticospinal tract*
- The **lateral corticospinal tract** is a major **motor pathway** originating in the cerebral cortex and responsible for voluntary movement.
- Damage to this tract would cause **motor deficits** (e.g., weakness, spasticity) and would not explain the isolated loss of fine touch sensation.
Question 58: A 27-year-old woman comes to the clinic for blisters on both hands. The patient has a past medical history of asthma, eczema, and a car accident 2 years ago where she sustained a concussion. She also reports frequent transient episodes of blurred vision that clear with artificial tears. When asked about her blisters, the patient claims she was baking yesterday and forgot to take the pan out with oven gloves. Physical examination demonstrates weeping blisters bilaterally concentrated along the palmar surfaces of both hands and decreased pinprick sensation along the arms bilaterally. What is the most likely explanation of this patient’s symptoms?
A. Brain contusion
B. Syringomyelia at the lumbar region
C. Syringomyelia at the cervico-thoracic region (Correct Answer)
D. Multiple sclerosis
E. Sjogren syndrome
Explanation: ***Syringomyelia at the cervico-thoracic region***
- The presence of **painless burns/blisters** (due to **loss of pain and temperature sensation**) on the hands, coupled with **decreased pinprick sensation bilaterally along the arms**, strongly suggests involvement of the **cervical and thoracic spinal cord**, characteristic of syringomyelia.
- The history of a **concussion** from a car accident 2 years ago could be a predisposing factor leading to or exacerbating a Chiari malformation, which is often associated with syringomyelia.
*Brain contusion*
- A **brain contusion** would typically cause focal neurological deficits based on the affected brain region, but it would not explain the **bilateral loss of pain and temperature sensation** in the arms or palmar blistering.
- While a concussion history is provided, contusions do not usually present with the specific type of sensory deficit seen here.
*Syringomyelia at the lumbar region*
- **Syringomyelia at the lumbar region** would primarily cause symptoms in the **lower extremities**, such as leg weakness, pain, and sensory loss in the legs and feet.
- It would not explain the **bilateral decreased pinprick sensation along the arms** or the blisters on the hands.
*Multiple sclerosis*
- **Multiple sclerosis** often presents with fluctuating neurological symptoms, including **blurred vision**, but the characteristic **dissociated sensory loss** (loss of pain and temperature with preserved touch) and **painless burns** are not typical primary presentations.
- Sensory deficits in MS are usually more varied and can include numbness, tingling, or electric shock sensations rather than purely dissociated loss.
*Sjogren syndrome*
- **Sjögren's syndrome** is an autoimmune disorder primarily affecting exocrine glands, leading to **dry eyes** (which could cause blurred vision that improves with artificial tears) and dry mouth.
- It does not explain the **painless burns** or the bilateral **loss of pain and temperature sensation** in the upper extremities.
Question 59: A 60-year-old man comes to the physician because his wife has noticed that his left eye looks smaller than his right. He has had worsening left shoulder and arm pain for 3 months. He has smoked two packs of cigarettes daily for 35 years. Examination shows left-sided ptosis. The pupils are unequal but reactive to light; when measured in dim light, the left pupil is 3 mm and the right pupil is 5 mm. Which of the following is the most likely cause of this patient's ophthalmologic symptoms?
A. Aneurysm of the posterior cerebral artery
B. Infiltration of the cervical plexus
C. Dissection of the carotid artery
D. Thrombosis of the cavernous sinus
E. Compression of the stellate ganglion (Correct Answer)
Explanation: ***Compression of the stellate ganglion***
- The patient's symptoms (left-sided ptosis, miosis, and anhidrosis, indicated by unequal pupils with the left pupil smaller in dim light) are classic for **Horner's syndrome**.
- Given the history of smoking and arm/shoulder pain, the most likely cause is a **Pancoast tumor** (apical lung cancer) compressing the **stellate ganglion** within the cervical sympathetic chain.
*Aneurysm of the posterior cerebral artery*
- This would typically present with symptoms related to occipital lobe dysfunction, such as **visual field defects**, rather than Horner's syndrome.
- While aneurysms can cause neurological deficits, this specific presentation is not characteristic of posterior cerebral artery involvement.
*Infiltration of the cervical plexus*
- The cervical plexus primarily innervates the muscles and skin of the neck and shoulder; infiltration would typically cause **motor weakness** or **sensory changes** in these areas.
- While shoulder and arm pain are present, cervical plexus involvement alone does not explain the specific constellation of **Horner's syndrome**.
*Dissection of the carotid artery*
- Carotid artery dissection can cause Horner's syndrome, but it is typically accompanied by **unilateral neck pain**, **headache**, and sometimes symptoms of **cerebral ischemia** (e.g., transient ischemic attack or stroke).
- The patient's chronic shoulder and arm pain and smoking history point away from dissection as the primary cause.
*Thrombosis of the cavernous sinus*
- Cavernous sinus thrombosis would likely present with more severe symptoms, including **painful ophthalmoplegia** (paralysis of eye muscles), **chemosis**, and **proptosis**, due to involvement of cranial nerves III, IV, V1, V2, and VI.
- The patient's symptoms are limited to Horner's syndrome and do not suggest widespread cranial nerve involvement.
Question 60: A 60-year-old African American woman presents to her ophthalmologist with blurry vision. She reports a 2-month history of decreased vision primarily affecting her right eye. Her past medical history is notable for type 1 diabetes and hypertension. She takes insulin and enalapril. She has a 40-pack-year smoking history and drinks a glass of wine at dinner each night. Her family history is notable for glaucoma in her mother and severe diabetes complicated by nephropathy and retinopathy in her father. Her temperature is 99°F (37.2°C), blood pressure is 134/82 mmHg, pulse is 88/min, and respirations are 18/min. On exam, she is well-appearing and in no acute distress. The physician asks the patient to look forward and shines a penlight first in one eye, then the other, alternating quickly to observe the pupillary response to the light. When the light is shined in the right eye, both pupils partially constrict. When the light is shined in the left eye, both pupils constrict further. When the light is moved back to the right eye, both eyes dilate slightly to a partially constricted state. Where is the most likely site of this patient’s lesion?
A. Lateral geniculate nucleus
B. Lens
C. Oculomotor nerve
D. Ciliary ganglion
E. Optic nerve (Correct Answer)
Explanation: ***Optic nerve***
- The alternating pupillary response, where shining light in the affected right eye causes less constriction than in the left eye, even though both pupils constrict, points to a **Relative Afferent Pupillary Defect (RAPD)**, also known as a **Marcus Gunn pupil**.
- An RAPD indicates a lesion in the **afferent visual pathway** anterior to the optic chiasm, most commonly the optic nerve, as it reduces the input signal from the affected eye to the brainstem.
*Lateral geniculate nucleus*
- A lesion in the **lateral geniculate nucleus (LGN)** would cause a visual field defect, but typically would not present with an RAPD because the pupillary light reflex pathway largely bypasses the LGN.
- The afferent pupillary fibers synapse in the **pretectal nucleus** before reaching the Edinger-Westphal nucleus, not the LGN.
*Lens*
- Problems with the **lens**, such as cataracts, cause blurry vision due to light scattering but do not affect the afferent pupillary pathway or cause an RAPD.
- The lens focuses light onto the retina; it is not involved in transmitting signals for the pupillary light reflex.
*Oculomotor nerve*
- A lesion in the **oculomotor nerve (CN III)** would affect the efferent pupillary pathway, leading to a **dilated pupil** in the affected eye, often with impaired extraocular movements, which is not described.
- The oculomotor nerve carries parasympathetic fibers responsible for pupillary constriction.
*Ciliary ganglion*
- A lesion in the **ciliary ganglion** would also affect the efferent pupillary pathway, causing a **dilated pupil** and sluggish or absent light reflex on the affected side (tonic pupil).
- This is a post-ganglionic parasympathetic lesion, which would present differently from the observed RAPD.
