Subacute combined degeneration of spinal cord

Subacute combined degeneration of the spinal cord (SCD) is a form of demyelination that affects the spinal cord, specifically the posterior and lateral columns. This condition is most commonly associated with a deficiency in Vitamin B12 (cobalamin), which is crucial for the proper functioning and maintenance of the nervous system. SCD is characterized by a triad of symptoms: weakness or paralysis, abnormal sensations (paresthesia), and ataxia, which can lead to difficulty in coordination and balance.

Etiology

The primary cause of subacute combined degeneration of the spinal cord is a deficiency in Vitamin B12. This deficiency can result from various factors including pernicious anemia, strict vegetarian diets, or malabsorption syndromes such as Crohn's disease or celiac disease. Vitamin B12 is essential for myelin synthesis, and its deficiency leads to demyelination in the spinal cord and peripheral nerves.

Pathophysiology

Vitamin B12 plays a critical role in the methylation of myelin sheath phospholipids and the synthesis of nucleic acids. Its deficiency disrupts these processes, leading to the degeneration of the myelin sheath in the spinal cord's posterior and lateral columns. This degeneration affects both the sensory and motor pathways, leading to the clinical manifestations of SCD.

Clinical Features

Patients with SCD typically present with a combination of neurological symptoms, which may include:

• Weakness or paralysis of the lower limbs
• Paresthesia (abnormal sensations) such as tingling or numbness
• Ataxia (impaired balance and coordination)
• Muscle stiffness and spasticity
• Impaired vibration sense and proprioception (sense of body position)
• Mental changes, including memory loss, irritability, and depression in advanced cases

Diagnosis

The diagnosis of SCD is based on clinical presentation, laboratory tests, and imaging studies. Key diagnostic tests include:

• Blood tests showing Vitamin B12 deficiency
• Elevated levels of homocysteine and methylmalonic acid, which are markers of Vitamin B12 deficiency
• Magnetic resonance imaging (MRI) of the spinal cord showing characteristic changes in the posterior and lateral columns
• Electromyography (EMG) and nerve conduction studies (NCS) to assess the extent of nerve damage

Treatment

Treatment of SCD focuses on addressing the underlying Vitamin B12 deficiency and alleviating symptoms. This typically involves:

• High-dose Vitamin B12 supplementation, either orally or through intramuscular injections
• Supportive care for symptoms, such as physical therapy for weakness and ataxia
• Treatment of the underlying cause of Vitamin B12 deficiency, such as pernicious anemia or malabsorption syndromes

Prognosis

With timely diagnosis and treatment, many patients experience significant improvement in symptoms, although some degree of neurological impairment may persist. Early intervention is crucial to prevent irreversible damage to the nervous system.

Prevention

Prevention of SCD involves ensuring adequate intake of Vitamin B12 through diet or supplements, especially in populations at risk of deficiency such as vegetarians or individuals with malabsorption syndromes.