By Marcello Cherchi, MD PhD
Vitamin B12, also called cyanocobalamin, is usually obtained in the diet from animal products (meat, poultry, fish, eggs, dairy products). A deficiency of vitamin B12 can occur due to inadequate diet, or due to a variety of malabsorption syndromes (Gueant, Gueant-Rodriguez et al. 2022)
Vitamin B12 is essential for cellular energy metabolism, so a deficiency of vitamin B12 can have a wide variety of presentations. As far as otoneurology is concerned, the main mechanisms by which vitamin B12 deficiency can interfere with a person’s equilibrium include:
- Spinal cord subacute combined degeneration (Kostick, Chen et al. 2022)
- Peripheral neuropathy (Solomon 2016)
- Ocular motor disturbances
Ocular motor disturbances are not commonly documented in vitamin B12 deficiency, but may also be underreported if the clinical picture is dominated by other features (such as spinal cord subacute combined degeneration).
There are several case reports and case series in the literature (Puri, Chaudhry et al. 2006, Akdal, Yener et al. 2007, Ouchi, Ishikawa et al. 2020) regarding ocular motor abnormalities observed in vitamin B12 deficiency. Most cases involve spontaneous down beat nystagmus in primary position of gaze. A smaller proportion of cases present with internuclear ophthalmoplegia (Akdal, Yener et al. 2007). One case report noted spontaneous up beat nystagmus in primary position of gaze (Ouchi, Ishikawa et al. 2020).
Treatment of significant vitamin B12 deficiency is usually initiated with intramuscular injections, eventually transitioning to oral supplementation. If this fails, then a search is usually undertaken for a vitamin B12 malabsorption syndrome.
References
Akdal G, Yener GG, Ada E, Halmagyi GM (2007) Eye movement disorders in vitamin B12 deficiency: two new cases and a review of the literature. Eur J Neurol 14: 1170-2. doi: 10.1111/j.1468-1331.2007.01824.x
Gueant JL, Gueant-Rodriguez RM, Alpers DH (2022) Vitamin B12 absorption and malabsorption. Vitam Horm 119: 241-274. doi: 10.1016/bs.vh.2022.01.016
Kostick N, Chen E, Eckert T, Sirotkin I, Baldinger E, Frontera A (2022) Clinical Presentation of Subacute Combined Degeneration in a Patient With Chronic B12 Deficiency. Fed Pract 39: 142-146. doi: 10.12788/fp.0228
Ouchi H, Ishikawa K, Inoue K, Shibano K, Hara K (2020) Primary Position Upbeat Nystagmus with Low Serum Vitamin B12. Intern Med 59: 3229-3233. doi: 10.2169/internalmedicine.5241-20
Puri V, Chaudhry N, Satyawani M (2006) Down beat nystagmus in vitamin B 12 deficiency syndrome. Electromyogr Clin Neurophysiol 46: 101-4.
Solomon LR (2016) Vitamin B12-responsive neuropathies: A case series. Nutr Neurosci 19: 162-8. doi: 10.1179/1476830515Y.0000000006
