Subacute combined degeneration

Clinical History

An 82-year-old man, with a history of type 2 diabetes, macrocytic anaemia, hyperhomocysteinaemia treated with folic acid, complained of fatigue, lower and upper limbs paresthesia, lower limbs weakness and pain.
The neurological examination showed hypoesthesia with D12 level, loss of deep/superficial sensitivity and reflexes in his lower limbs, unsteady gait.

Imaging Findings

Because of the patient’s neurological symptoms, MRI of the cervical and dorsal spine was performed.
An abnormal strip-like signal area, corresponding to the posterior columns and extending along the entire cervico-dorsal cord was hypointense on the T1-W images (Fig. 1) and hyperintense on T2-W images (Fig. 2). The axial images revealed symmetric signal hyperintensity on T2-W images within the posterior columns (inverted V sign) and in lateral columns (Fig. 3). Sagittal (Fig. 4) and axial (Fig. 5) contrast enhanced T1-W images showed mild contrast enhancement.
These findings suggested a demyelinating myelopathy secondary to metabolic causes/vitamins deficiency.
After receiving cobalamin (Vitamin B12) intramuscular injections 1 mg/day, the patient had a slow but progressive neurological improvement.

Discussion

In the presence of macrocytic anaemia and neurological symptoms like limbs weakness and paresthesia, cobalamin (vitamin B12) deficiency should be suspected. Sometimes neurological symptoms are not associated with anaemia [1]. They usually appear when the value of cobalamin falls below 100 pg/ml, but there is not always any parallel between them. The level of methylmalonic acid (MMA) and homocysteine increases when the tissue reserve of cobalamin drops, thereby more closely reflecting cobalamin deficiency [2].
Cobalamin deficiency is common in older people [2] as a response to insufficient intake or malabsorption [3]. It may be also a consequence of genetic deficiency of methylmalonyl-CoA mutase enzyme [1].
Neurological complications seem associated with elevated levels of MMA, which is toxic to myelin sheaths and axons [4]. Demyelinated lesions may also be due to an overproduction of myelinolytic Tumour Necrosis Factor a (TNF-a) and a reduced synthesis of the neurotrophic agents Epidermal Growth Factor (EGF) and Interleukin-6 (IL-6) as a consequence of cobalamin deficiency [5].
Pathological lesions involve the fibres of the posterior columns at the cervicodorsal and midthoracic level [5]. As the disease progresses lesions may involve the lateral and anterior columns [1].
Myelopathy due to cobalamin deficiency is called subacute combined degeneration (SCD). SCD can also result from folate deficiency and nitrous oxide anesthesia [5].
The clinical manifestations range from impaired positional sense and vibration up to weakness of the extremities, unsteady gait, spastic paresis or tetraparesis [2].
The MRI findings suggest the diagnosis of SCD. An abnormal strip-like signal area extending along the cord, hypointense on the T1-weighted and hyperintense on T2-weighted MRI, with mild contrast enhancement are the most common findings [1, 6, 7]. Axial spine MRI displays T2 hyperintensity with a characteristic “inverted V” or inverted “rabbit ears” appearance due to the characteristic involvement of the posterior columns [6, 7].
All patients with cobalamine deficiency should be investigated to determine the cause and wheter it might be reversible. The traditional replacement therapy for cobalamine deficiency consists of intramuscular doses of 1,000 mcg/day for a week, then 1,000 mcg/week for a month and, subsequently, 1,000 mcg/month for life [3].
Early diagnosis and treatment are important, especially in severe cases. Recovery may be complete if symptoms have only been present for a few weeks before the start of treatment. If the interval has been longer, treatment may improve symptoms but imaging abnormalities may not completely resolve [2, 6].

Differential Diagnosis List

Final Diagnosis

Cobalamin-deficiency (Vitamin B12) myelopathy: Subacute combined degeneration

URL:	https://eurorad.org/case/10531
DOI:	10.1594/EURORAD/CASE.10531
ISSN:	1563-4086