Appearance of hypersegmented neutrophils in the peripheral blood associated with subacute combined degeneration of the spinal cord due to nitrous oxide abuse

Abstract

A 25-year-old man following 1 year of recreational nitrous oxide (N2O) use presented with quadriplegia and decreased sensation in a glove and stocking distribution. The weakness distally was 2/5 and proximally 2–3/5. The spinal cord lesions showed an increased signal in a V-shape within the posterior column on T2-weighted magnetic resonance imaging (MRI) extending posteriorly from the C1–C2 level to the C5 level. Laboratory tests showed: white cell count 4.39 × 109/l, red cell count 3.95 × 109/l, haemoglobin concentration 133 g/l, haematocrit 0.39 l/l, mean corpuscular volume 99.4 fl (normal range 82–100), mean corpuscular haemoglobin 33.8 pg, mean corpuscular haemoglobin concentration 340 g/l, red cell distribution width 16.2% (9.0–17.0), platelet count 175 × 109/l, serum folate 22.82 ng/ml (5.90–24.80), homocysteine 11.3 μmol/l (0.0–20.0), methylmalonic acid 296 nmol/l (73–376), vitamin B12 312 pg/ml (180–914) and thiamine 165.3 nmol/l (66.5–200). The differential white cell count was normal but a peripheral blood film showed hypersegmented neutrophils, 19% having 6 lobes (normal 1–5) (images, ×100 objective, Wright–Giemsa stain). Neutrophil alkaline phosphatase was normal. The morphology of mature red blood cells showed no obvious abnormality. The patient received intensive physiotherapy and vitamin B12 therapy. At outpatient review 6 weeks later, his symptoms had improved considerably. Neurological examination was normal apart from a mild hyporeflexia of the lower limbs. His peripheral blood film no longer showed neutrophil hypersegmentation. The clinical diagnosis of nitrous oxide abuse causing subacute combined degeneration of the spinal cord mainly depends on a history of N2O inhalation. However patients who are generally young men may conceal the N2O abuse history. Hence, clinical staff should be aware not only of the various presentations of neurotoxicity, but also the peripheral blood features related to N2O abuse.