Lateral Medullary Infarction: Expected Neurologic Deficits
The correct answer is: Left hemiataxia, left miosis, decreased pinprick sensation in his left face and right hemibody, and hoarseness.
Classic Lateral Medullary Syndrome Presentation
The lateral medullary syndrome (Wallenberg syndrome) presents with a characteristic pattern of ipsilateral cerebellar signs, ipsilateral Horner syndrome, crossed sensory deficits (ipsilateral face, contralateral body), and bulbar symptoms 1.
Expected Findings with LEFT Lateral Medullary Infarction:
Ipsilateral (Left-sided) Deficits:
- Left hemiataxia - due to involvement of the inferior cerebellar peduncle and spinocerebellar tracts 1, 2
- Left miosis (Horner syndrome) - from disruption of descending sympathetic fibers 1, 3
- Decreased pinprick sensation in the LEFT face - caused by damage to the spinal trigeminal nucleus and tract 1
- Hoarseness and dysphagia - resulting from nucleus ambiguus involvement affecting cranial nerves IX and X 2, 3
Contralateral (Right-sided) Deficits:
- Decreased pinprick sensation in the RIGHT hemibody - due to spinothalamic tract involvement before it has crossed 1, 2
Why Motor Weakness is NOT Expected
Severe hemiparesis is NOT a typical feature of lateral medullary infarction because the corticospinal tracts run in the ventral medulla (pyramids), while lateral medullary infarction affects the dorsolateral medulla 4, 3.
- Contralateral hemiparesis only occurs when the infarct extends caudally to involve the pyramidal tracts before decussation, which is rare and represents Babinski-Nageotte syndrome 4, 3
- This atypical presentation with hemiparesis is explicitly noted as unusual in the literature 5, 4
Anatomic Localization Principles
The crossed sensory pattern is pathognomonic for lateral medullary syndrome 1:
- Pain/temperature fibers from the face (trigeminal) remain ipsilateral in the spinal trigeminal tract
- Pain/temperature fibers from the body (spinothalamic) have already crossed at spinal levels and ascend contralaterally
- Therefore: ipsilateral facial numbness + contralateral body numbness 1, 2
Clinical Variability Caveat
While the classic triad is well-described, variability in presentation is the rule rather than the exception 1, 2. The specific deficits depend on:
- Rostral versus caudal location within the medulla 2
- Extent of ischemia (anteromedial, anterolateral, lateral, or posterior regions) 2
- Severity of involvement of specific nuclei 2
However, the fundamental pattern of ipsilateral cerebellar signs, ipsilateral Horner syndrome, and crossed sensory deficits remains the diagnostic hallmark 1.