Can vitamin B12 deficiency cause reduced deep tendon reflexes?

Vitamin B12 Deficiency and Reduced Deep Tendon Reflexes

Yes, vitamin B12 deficiency can cause reduced deep tendon reflexes due to its effects on the peripheral nervous system and spinal cord. 1

Neurological Effects of B12 Deficiency

Vitamin B12 deficiency causes extensive neurological damage through several mechanisms:

• Demyelination: B12 deficiency results in extensive demyelination in the central nervous system (particularly the spinal cord) and peripheral nervous system 1
• Axonal degeneration: Significant damage occurs to nerve fibers, with axonal degeneration particularly affecting distal afferent fibers of dorsal root ganglion neurons 1
• Progressive neurological symptoms: As deficiency progresses, symptoms become more severe 1, 2

Specific Neurological Manifestations

B12 deficiency affects the neuromuscular system in multiple ways:

• Abnormal reflexes: Deep tendon reflexes are commonly reduced or absent 1, 3
• Sensory deficits: Decline in proprioceptive, vibratory, tactile, and nociceptive sensation 1
• Motor function: Muscle weakness, spasticity, and gait ataxia 1, 2
• Nerve conduction: Reduced nerve conduction velocity, indicating direct detrimental effects on peripheral motor function 1

Clinical Evidence

A case report of a 22-year-old male with vitamin B12 deficiency demonstrated:

• Absent deep tendon reflexes in all four extremities
• Axonal-type sensorimotor polyneuropathy on nerve conduction studies
• Gradual recovery of reflexes and muscle power following B12 supplementation 3

Pathophysiological Mechanism

The reduced deep tendon reflexes in B12 deficiency occur due to:

1. Peripheral nerve damage: Demyelination and axonal degeneration in peripheral nerves disrupt normal reflex arcs 1, 2
2. Spinal cord involvement: Subacute combined degeneration of the spinal cord affects posterior and lateral columns 4, 5
3. Proprioceptive loss: Impaired proprioception contributes to reflex abnormalities 2

Timing and Progression

• Neurological symptoms, including reflex abnormalities, may appear before hematological changes 2
• If B12 deficiency is allowed to progress for longer than three months, it may produce permanent degenerative lesions of the spinal cord 4, 5
• Early symptoms often affect the peripheral nervous system with loss of motor function 1

Diagnosis and Treatment

Diagnosis

• Measure serum B12 levels (deficiency typically <180 pg/mL) 6
• For borderline levels (180-350 pg/mL), measure methylmalonic acid and homocysteine 2, 6
• Neurological examination should include assessment of deep tendon reflexes 7

Treatment

• High-dose oral vitamin B12 (1-2 mg or 1000-2000 mcg daily) is effective for most patients 2, 6
• Intramuscular administration should be considered for patients with severe deficiency or neurological manifestations 6
• Treatment should be initiated promptly to prevent irreversible neurological damage 2, 4

Important Considerations

• Folic acid should not be administered alone before treating B12 deficiency, as it may mask hematological symptoms while allowing neurological damage to progress 2, 4, 5
• Recovery of neurological function may take months and follow a specific sequence, with proximal muscles recovering before distal ones 3
• Some neurological damage may be irreversible if treatment is delayed 2, 4, 5

Early recognition and treatment of B12 deficiency is crucial to prevent permanent neurological damage, including persistent abnormalities in deep tendon reflexes.