A 10-year-old boy presented with progressive difficulty in walking for 1 year with
preserved cognition. On examination, his head circumference was 51 cm. He had an expressionless
face, spastic speech, spastic gait, and impaired finger tapping. Other systemic examination
was unremarkable. Kayser–Fleischer rings were absent. An magnetic resonance imaging
(MRI) of brain showed brainstem and spinal cord involvement ([Fig. 1]). Evaluation for antinuclear antibodies, serum copper and ceruloplasmin, ammonia,
lactate, aquaporin-4 antibody, tandem mass spectrometry, and urine for organic acids
were within normal limits. Biotinidase was found to be severely deficient (0.69 nmol/mL;
range: 5–9 nmol/mL).The spasticity and gait normalized after three months of biotin
therapy (20 mg/day)
Fig. 1 (A) Magnetic Resonance Imaging showing T2 hyperintensities in periventricular white
matter, (B) dorsal pons, (C) In Axial-T2 weighted MRI image of cervical cord, this hyperintensity was confined
to anterior part mimicking “Owl’s eye”. (D, E) Diffusion restriction was seen in fornix. (F) MRI T2-weighted film, sagittal view of spine, showing longitudnal central T2 hyperintensity
from medulla to T1.
The clinical and radiological presentations of late-onset biotinidase deficiency are
variable. MRI abnormalities are predominantly seen in white matter tracts involving
septum pellucidum, corpus callosum, fornix, thalamus, brainstem, periaqueductal gray
matter, optic tracts,[1] hippocampus, and cerebellar white matter.[2] Diffusion restriction in white matter tracts has been attributed to vacuolating
myelinopathy seen in tissue specimens.[3] Isolated cervicodorsal spine involvement may occur, though whole cord involvement
has also been described.[1] Spinal involvement may be diffuse[1] or may have selective tract involvement.[4] Bhat et al have described a child with myelopathy and selective involvement of anterior,
lateral, and posterior columns.[4] Honavar et al have described selective involvement of anterior and posterior column
on neuropathology.[2] The spinal involvement of the index child with selective tract involvement has been
radiological described as “Owl's eye appearance”, which is typically seen in anterior
horn cell myelitis but also described with respect to spinal cord infarction, radiation
myelopathy, and fibrocartilaginous emboli.[5]
To conclude, biotinidase deficiency is worth ruling out in all the cases of unexplained
spastic quadriparesis or paraparesis as treatment is rewarding.
