Question
A 39-year-old woman presents with sudden onset tingling and weakness affecting her left arm and leg. One year ago, she experienced transient visual blurring that resolved without treatment. She has a history of mild hypertension and drinks alcohol socially.
On examination, there is increased tone and weakness in the left limbs, an extensor plantar response, and neck flexion produces a brief electric shock sensation down the spine. Fundoscopy is normal. MRI brain shows white matter lesions in periventricular and cortical regions, all appearing of identical signal intensity.
Which of the following additional findings would most strongly support the suspected diagnosis?
a. Reduced activity and shrinkage of mammillary bodies
b. Symmetrical signal changes in posterior thalamic nuclei
c. Marked shrinkage of medial temporal lobes
d. Prolonged latency on visual evoked response testing
e. Predominant anterior cerebral atrophy with sparing of posterior cortex
Answer
d. Prolonged latency on visual evoked response testing
Detailed Explanation
This clinical picture is classic for Multiple Sclerosis (MS).
Key clinical clues:
- Relapsing neurological deficits → weakness + previous visual symptoms
- Optic neuritis (history of blurred vision)
- Upper motor neuron signs → spasticity, Babinski
- Lhermitte’s sign → electric shock on neck flexion
- MRI lesions → periventricular + juxtacortical
👉 These establish dissemination in space
❌ But all lesions same intensity → no dissemination in time yet
Why Visual Evoked Potentials (VEP) help:
- Detect subclinical optic nerve demyelination
- Even if patient has no current visual symptoms
- Delayed latency = previous demyelination episode
👉 This provides dissemination in time, which is essential for MS diagnosis
Why other options are wrong:
- Mammillary body changes → seen in Wernicke’s encephalopathy
- Pulvinar sign → seen in Variant Creutzfeldt-Jakob disease
- Medial temporal atrophy → Alzheimer’s disease
- Frontal/temporal atrophy → Frontotemporal dementia
Cheat Sheet for Exam
Multiple Sclerosis Diagnosis
- Requires:
- Dissemination in space
- Dissemination in time
MRI Findings
- Periventricular plaques
- Juxtacortical lesions
- Dawson’s fingers
Investigations
- MRI → primary
- CSF → oligoclonal bands
- VEP → delayed latency
Key Signs
- Optic neuritis
- Lhermitte’s sign
- UMN signs
Flash Cards
Q1: What are the two essential criteria for MS diagnosis?
A: Dissemination in space and time
Explanation: Must show lesions in different CNS areas and at different times
Q2: What does Lhermitte’s sign indicate?
A: Cervical cord demyelination
Explanation: Electric shock sensation on neck flexion
Q3: What does delayed VEP suggest?
A: Previous optic nerve demyelination
Explanation: Helps prove dissemination in time
Q4: What CSF finding is typical in MS?
A: Oligoclonal bands
Explanation: Reflect intrathecal IgG synthesis
Q5: What are Dawson’s fingers?
A: Periventricular lesions perpendicular to corpus callosum
Explanation: Classic MRI feature of MS
MCQs (Challenging Level)
MCQ 1
A patient with suspected MS has MRI lesions but all appear the same age. What is the best next step?
a. Repeat MRI in 6 months
b. CSF protein measurement
c. Visual evoked potentials
d. EEG
e. PET scan
Answer: c. Visual evoked potentials
Explanation: Detects prior demyelination → proves dissemination in time immediately.
MCQ 2
Which of the following is FALSE regarding MS?
a. Oligoclonal bands are seen in CSF but not serum
b. MRI lesions are typically periventricular
c. VEP latency is shortened
d. Lhermitte’s sign may occur
e. Optic neuritis is common
Answer: c. VEP latency is shortened
Explanation: Latency is prolonged, not shortened.
MCQ 3
Which feature best distinguishes MS from acute disseminated encephalomyelitis (ADEM)?
a. Presence of demyelination
b. MRI lesions
c. Dissemination in time
d. White matter involvement
e. Neurological deficits
Answer: c. Dissemination in time
Explanation: ADEM is monophasic; MS is relapsing.
MCQ 4
A patient has periventricular lesions and optic neuritis. What is the most specific additional test?
a. Serum IgG
b. Visual evoked potential
c. CT brain
d. Nerve conduction study
e. Muscle biopsy
Answer: b. Visual evoked potential
Explanation: Detects subclinical optic nerve involvement.
MCQ 5
Which MRI feature is most characteristic of MS?
a. Basal ganglia calcification
b. Diffuse cortical atrophy
c. Dawson finger lesions
d. Cerebellar infarcts
e. Thalamic hemorrhage
Answer: c. Dawson finger lesions
Explanation: Perpendicular periventricular plaques are classic.
MCQ 6
Which condition shows pulvinar sign on MRI?
a. MS
b. Alzheimer’s disease
c. Variant CJD
d. Wernicke’s encephalopathy
e. FTD
Answer: c. Variant CJD
Explanation: Bilateral thalamic hyperintensity.
Summary for Quick Exam Revision
Multiple sclerosis is an autoimmune demyelinating disease characterized by episodes of neurological dysfunction separated in time and space. Typical clinical features include optic neuritis, limb weakness, sensory disturbances, and Lhermitte’s sign. MRI shows periventricular and juxtacortical plaques, often described as Dawson’s fingers. Diagnosis requires demonstration of both dissemination in space and time; when MRI shows lesions of the same age, additional evidence such as delayed visual evoked potentials can confirm prior demyelination. CSF oligoclonal bands further support the diagnosis. Visual evoked potentials are particularly useful for detecting subclinical optic nerve involvement. Differentials such as Wernicke’s encephalopathy, variant CJD, Alzheimer’s disease, and frontotemporal dementia have distinct imaging patterns and clinical presentations. Early diagnosis is crucial as treatment delays can worsen long-term disability.