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.