What is the diagnostic algorithm for Central Pontine Myelinolysis (CPM)?

Diagnostic Algorithm for Central Pontine Myelinolysis

The diagnosis of CPM requires MRI brain imaging with characteristic pontine signal changes on T2-weighted sequences in a patient with risk factors (particularly hyponatremia or rapid sodium correction), combined with compatible clinical features ranging from subtle brainstem signs to locked-in syndrome. 1, 2

Clinical Suspicion Criteria

Suspect CPM when the following features are present:

• Electrolyte disturbance, primarily hyponatremia (serum sodium typically <120 mEq/L) 1
• Progressive neurologic deficits developing days to weeks after sodium correction, potentially progressing to "locked-in" syndrome 1
• History of chronic alcoholism (present in majority of cases but not required) 1, 3
• Recent rapid correction of hyponatremia (iatrogenic precipitation through inappropriate rehydration) 1

Clinical Presentation Spectrum

The neurologic manifestations vary widely in severity 4:

• Severe presentations: Spastic tetraparesis, pseudobulbar palsy, dysarthria, encephalopathy, locked-in syndrome, or coma 2, 5
• Mild presentations: Latent pyramidal tract signs, discrete ocular motor abnormalities (horizontal gaze palsy, ophthalmoparesis), cranial nerve palsies 4, 6
• Neuropsychiatric presentations: Acute psychosis, paranoia, hallucinations, personality changes, or catatonia (may occur without focal deficits) 5
• Asymptomatic cases: Imaging findings without clinical deficits (rare but documented) 3

Imaging Algorithm

Primary Diagnostic Modality

MRI brain is the diagnostic test of choice and should be obtained when CPM is suspected 2:

• T2-weighted and FLAIR sequences demonstrate characteristic hyperintensity in the central pons 2
• MRI sensitivity: Can detect lesions even when CT is normal 2
• CT limitations: Initial CT may be completely normal and misses small pontine lesions in up to 25% of cases 6, 2

Timing Considerations

• Early imaging may be negative: Initial MRI can be unremarkable in the first days after symptom onset 5
• Repeat imaging: If clinical suspicion remains high despite negative initial MRI, repeat imaging 1-2 weeks later is warranted 5
• Serial imaging: Follow-up MRI at 6 months and 18 months can demonstrate progressive resolution correlating with clinical recovery 2

Imaging Characteristics

• Location: Central basis pontis with characteristic symmetric involvement 1, 2
• Extrapontine involvement: May occur concurrently (extrapontine myelinolysis affecting basal ganglia, thalamus, cerebellum) 4
• Contrast enhancement: Typically not present (helps differentiate from pontine tuberculoma which shows ring enhancement) 6

Critical Differential Diagnosis

When evaluating pontine lesions on imaging, consider:

• Pontine gliomas: Can mimic CPM on imaging; distinction is critical as management and prognosis differ significantly 6
• Pontine tuberculomas: Show ring enhancement with surrounding edema, associated with systemic TB, lymphocytic CSF pleocytosis 6
• Progressive multifocal leukoencephalopathy (PML): Subacute onset, diffuse lesions, typically in immunocompromised patients 7

Diagnostic Workup

Laboratory Assessment

• Serum sodium levels: Document current and recent values, calculate rate of correction 1
• Assess precipitating factors: Review diuretic use, fluid administration, underlying conditions 3

Neurological Examination

Focus on specific brainstem findings:

• Cranial nerve function: Particularly nerves V-VIII which traverse the pons 6, 8
• Motor examination: Assess for pyramidal tract signs, spasticity, tetraparesis 4
• Ocular motor function: Horizontal gaze palsy, ophthalmoparesis 6, 4
• Bulbar function: Dysarthria, dysphagia, pseudobulbar palsy 2
• Mental status: Screen for encephalopathy, psychosis, personality changes 5

Common Pitfalls

• Assuming normal CT excludes CPM: CT is insensitive; proceed to MRI if clinical suspicion exists 2
• Dismissing psychiatric symptoms: Acute psychosis may be the primary manifestation without focal deficits 5
• Single negative MRI: Early MRI may be normal; repeat if symptoms develop after sodium correction 5
• Overlooking asymptomatic cases: Imaging changes can occur without clinical deficits, particularly with slow correction 3
• Aggressive sodium correction: Even "gentle" correction can precipitate CPM in high-risk patients (chronic alcoholism, malnutrition) 3