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Subacute Combined Degeneration
KEY FACTS
Terminology
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Vitamin B12 deficiency produces selective degeneration of dorsal ± lateral spinal cord columns
Imaging
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Longitudinal dorsal cord T2 signal abnormality
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Axial image → “inverted V” or “inverted rabbit ears” within dorsal spinal cord
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± mild dorsal column enhancement
Top Differential Diagnoses
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Infectious myelitis
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HIV vacuolar myelopathy
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Varicella-Zoster/herpes
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Inflammatory demyelination
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Multiple sclerosis
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Acute disseminated encephalomyelitis
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Acute transverse myelitis
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Acute presentation → diffuse multisegmental cord hyperintensity, swelling
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Infarction, spinal cord
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Hyperacute presentation
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Copper deficiency, zinc toxicity (may look identical)
Pathology
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Malabsorption (most common)
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Metabolic conditions: Copper deficiency, nitrous oxide anesthesia susceptibility, transcobalamin II deficiency
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Clinical Issues
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Paraesthesia, stiffness, mild sensory ataxia, loss of position and vibration sense, spasticity, hyperreflexia
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Degree of resolution of clinical symptoms is inversely proportional to their duration and severity
Diagnostic Checklist
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Neurologic findings may precede anemia and may not completely resolve following treatment
Graphic shows dorsal column demyelination
secondary to vitamin B12 deficiency. Major clinical findings of dysesthesia, gait disturbance, and impairment of position and vibration sense in the lower ± upper limbs are secondary to dorsal column, lateral corticospinal tract, and sometimes lateral spinothalamic tract dysfunction.
secondary to vitamin B12 deficiency. Major clinical findings of dysesthesia, gait disturbance, and impairment of position and vibration sense in the lower ± upper limbs are secondary to dorsal column, lateral corticospinal tract, and sometimes lateral spinothalamic tract dysfunction.
Axial T2WI MR reveals T2 hyperintensity confined to the dorsal columns
in an “inverted V” configuration, characteristic of B12 deficiency.
in an “inverted V” configuration, characteristic of B12 deficiency.
Sagittal T1WI C+ MR reveals vague dorsal intramedullary enhancement
. Lack of cobalamin (required as a cofactor for conversion of methylmalonyl-CoA to succinyl-CoA) leads to accumulation of methylmalonyl-CoA, causing ↓ in normal myelin synthesis and incorporation of abnormal fatty acids into neuronal lipids.
. Lack of cobalamin (required as a cofactor for conversion of methylmalonyl-CoA to succinyl-CoA) leads to accumulation of methylmalonyl-CoA, causing ↓ in normal myelin synthesis and incorporation of abnormal fatty acids into neuronal lipids.
Axial MR reveals patchy enhancement in bilateral dorsal columns
, which reflects breakdown of the blood-cord barrier caused by perivascular demyelination and inflammation.
, which reflects breakdown of the blood-cord barrier caused by perivascular demyelination and inflammation.
TERMINOLOGY
Abbreviations
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Subacute combined degeneration (SCD)
Synonyms
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Combined system disease
Definitions
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Vitamin B₁₂ deficiency produces selective degeneration of dorsal ± lateral spinal cord columns
IMAGING
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