31st July 2023

A 64-year-old female with a background of vitiligo presents with tiredness

A 64-year-old female with a background of vitiligo presents with tiredness.

Blood tests show:
Hb 108g/L (115 – 160)
Ferritin 110 ng/mL (20 – 230)
Folate 1.9 nmol/L (>3)
Vitamin B12 88 (200 – 900)

She is started on folic acid 5mg OD but misses her appointment where she is due to be administered hydroxocobalamin IM.

Two months later, she presents with paraesthesia in her lower limbs. On examination, proprioception and vibration sense are diminished. The ankle jerk is absent, but the plantars show an extensor response.

What is the likely cause of the paraesthesia?

Select the SINGLE most appropriate option from the list below. Select ONE option only.