Macrocytic Anaemia Quiz

A young female presents with fatigue and tingling in her feet, which has been worsening over the last few months. She has some difficulty walking. On examination, she has hyperreflexia and diminished proprioception in her lower limbs. Other examination findings are shown below:

Image credit: Matthew Ferguson, CC BY-SA 3.0

What is the most likely diagnosis?

She has a postural BP drop of 30mmHg. Initial investigations show:

Haemoglobin 6.7g/dL (11.4-14.7)
MCV 128fL (83.0-95.5)
Platelets 23×10⁹/L (164-387)
WBC 2.4×10⁹/L (3.84-10.01)

Reticulocyte count: 0.38% (0.84-2.21%)
Reticulocyte count (absolute): 12×10⁹/L (38.30-110.50)

Sodium 120mmol/L (135-145)
Potassium 5.2mmol/L (3.5-5.0)
Urea 5.7mmol/L (2.0-7.5)
Creatinine 62µmol/L (50-90)

Albumin 31g/L (38-48)
Bilirubin, total 86µmol/L (5-30)
Bilirubin, conjugated 5µmol/L (0-5)
Bilirubin, unconjugated 81µmol/L (5-25)
AST 35U/L (10-50)
ALT 62U/L (10-70)
ALP 120U/L (40-130)
LDH 1750U/L (250-580)

B12 32pmol/L (135-675)
Folate 46nmol/L (7-45)

The peripheral blood film shows macrocytosis with macro-ovalocytes and hyper-segmented neutrophils.

What other investigations should be done at this point? Choose all that apply.

Why is her reticulocyte count low?

Where is B12 absorbed?

Her intrinsic factor antibodies are positive, and a short synacthen test reveals a blunted response. She is started on regular hydrocortisone with normalisation of her postural blood pressure and electrolytes and improvement in fatigue.

What is the immediate treatment of this patient’s B12 deficiency?

What should be monitored  during B12 replacement?