Subacute combined degeneration of the cord (SACD) is caused by vitamin B12 deficiency.
Most common in patients older than 40 and especially older than 60 7.
The clinical presentation of SACD is usually with loss of vibration and proprioception in the hands and feet, with eventual progression to sensory loss of all modalities, sensory gait ataxia, and distal muscle weakness, especially of the legs. Features of dementia may also become apparent.
SACD can be a sequelae of any cause of vitamin B12 deficiency. In the developed world where nutrition is generally adequate, it tends to result most commonly from pernicious anemia, but has other causes:
- Crohn disease and other causes of terminal ileitis (vitamin B12 is primarily absorbed at terminal ileum)
- use of proton pump inhibitors (acid is required to release vitamin B12 from meat)
- gastrointestinal surgery (especially if affecting the terminal ileum)
- celiac disease
- atrophic gastritis
- abuse of nitrous oxide (usually from recreational abuse) 3
Additionally, although uncommon, strict vegetarians or those who are undernourished may develop sufficient deficiencies to develop SACD.
Vitamin B12 levels may be normal in up to 30% of patients, and thus looking at levels of other more sensitive and specific biomarkers may be utilized instead:
- holotranscobalamin or active vitamin B12 (low)
- methylmalonic acid (high)
- homocysteine (high)
Most commonly there is symmetric bilateral high signal within the dorsal columns. This appearance has been described as the inverted "V" sign 4. The signal changes typically begin in the upper thoracic region, with ascending or descending progression 5.
The lateral corticospinal tracts, and sometimes lateral spinothalamic tract may also be involved. Although very unusual, there has been at least one described case of anterior cord involvement 6. Usually these areas have no contrast enhancement.
Often there is also accompanying cerebral white matter change. Both spinal and cerebral changes resolve after correction of vitamin B12 deficiency.
Treatment and prognosis
Management depends on the cause, but generally patients should be provided with intramuscular hydroxocobalamin injections, followed by oral supplementation. Additionally, patients should avoid using nitrous oxide.
Approximately half of all affected patients will completely recover 7.
Clinical differential diagnosis can be broad.
On imaging the differential includes:
- other nutritional deficiencies
- infectious causes
- inflammatory processes
- hereditary syndromes
- leukoencephalopathy with brainstem and spinal cord involvement and lactate elevation: characteristically also involves the cerebral white matter and the brainstem 10
- Friedreich ataxia: also causes cervical cord atrophy ('thinning') 10
- 1. Ravina B, Loevner LA, Bank W. MR findings in subacute combined degeneration of the spinal cord: a case of reversible cervical myelopathy. AJR Am J Roentgenol. 2000;174 (3): 863-5. AJR Am J Roentgenol (full text) - Pubmed citation
- 2. Srikanth SG, Jayakumar PN, Vasudev MK et-al. MRI in subacute combined degeneration of spinal cord: a case report and review of literature. Neurol India. 2002;50 (3): 310-2. Neurol India (link) - Pubmed citation
- 3. Shulman RM, Geraghty TJ, Tadros M. A case of unusual substance abuse causing myeloneuropathy. Spinal Cord. 2007 Apr;45(4):314-7. Epub 2006 Aug 8. Pubmed
- 4. Kumar, Ashok, and Amar Kumar Singh. "Teaching NeuroImage: Inverted V sign in subacute combined degeneration of spinal cord." Neurology 72.1 (2009): e4-e4.
- 5. Ketonen, Leena. Pediatric Brain and Spine: An Atlas of MRI and Spectroscopy. Berlin: Springer, 2005. pg 435, Print.
- 6. Karantanas AH, Markonis A, Bisbiyiannis G. Subacute combined degeneration of the spinal cord with involvement of the anterior columns: a new MRI finding. Neuroradiology. 2000;42 (2): 115-7. Pubmed citation
- 7. Spinal Cord Medicine. Demos Medical Publishing. ISBN:1933864192. Read it at Google Books - Find it at Amazon
- 8. Goodman BP, Chong BW, Patel AC et-al. Copper deficiency myeloneuropathy resembling B12 deficiency: partial resolution of MR imaging findings with copper supplementation. AJNR Am J Neuroradiol. 2006;27 (10): 2112-4. AJNR Am J Neuroradiol (full text) - Pubmed citation
- 9. Vorgerd M, Tegenthoff M, Kühne D, Malin JP. Spinal MRI in progressive myeloneuropathy associated with vitamin E deficiency. Neuroradiology. 38 Suppl 1: S111-3. Pubmed
- 10. Sen A, Chandrasekhar K. Spinal MR imaging in Vitamin B12 deficiency: Case series; differential diagnosis of symmetrical posterior spinal cord lesions. (2013) Annals of Indian Academy of Neurology. 16 (2): 255-8. doi:10.4103/0972-2327.112487 - Pubmed