Discussion: 
Subacute combined degeneration (SACD) of the spinal cord is the most frequent central neurological manifestation of vitamin B12 deficiency, disrupting the myelination process causing degeneration of the spinal cord’s dorsal and lateral white matter. [3] This usually contributes to a slow progressive paraparesis, symmetric dysesthesia, disruption of proprioception that can lead to sensory ataxia. 3-4 In more advanced cases, corticospinal tract involvement can cause abnormal deep tendon reflex, ultimately, spastic paraparesis and tetra-paresis in some cases, with autonomic dysfunction manifesting as urinary incontinence and sexual dysfunction. 4
Neurological manifestation in B12 deficiency in the absence of anemia is not uncommon, as our patient’s blood count showed macrocytosis with normal hemoglobin indices.
SACD is usually a gradually progressive process; however, sudden onset presentation warrants further workup to rule out mimics, such as spinal cord ischemia with posterior spinal artery involvement, which is uncommon due to the dual nature of these arteries and pial collateral network. 8
Since the early 1990s, MRI has been crucial in diagnosing vitamin B12-deficiency related central nervous system (CNS) – related complications and most conspicuously to rule out mimics, such as infectious and none infectious myelitis,
acute/subacute ischemic, or even demyelinating disease like multiple sclerosis. [4] SACD has typical radiological MRI findings, with a symmetrical high T2 signal intensity, confined mainly in the dorsal/posterior and lateral columns of cervical and thoracic spins, with an inverted V sign due to symmetrical involvement the structures mentioned above. [5]
Polat et al. conducted a retrospective study on 37 patients with biochemical evidence of B12 deficiency, showed significantly increased apparent diffusion coefficient (ACD) values in multiple brain areas such as the amygdala, hypothalamus, and striate cortex, but did not further look at radiological features in SACD. 1
Han Gao et al., in 2021, conducted a retrospective study on reactional Nitrous oxide (NO) related SACD compared to other SACD, showed MRI manifestation was more common among SACD-related NO with T2WI- high signal intensity in cervical and thoracic segments of the spinal cord, bearing in mind that Nitric oxide users had lower B12 levels. 7
Our patient had a sudden onset presentation that worsened over three days, of symmetrical dysesthesia and impaired sense of proprioception and vibration, found to have macrocytosis on peripheral smear with raised homocysteine level correlating with B12 deficiency without anemia.
His MRI showed an inverted V sign and high signal in thoracic spine segments on DWI sequence; that his symptoms resolved with adequate B12 replacement.