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Maple syrup urine disease

Maple syrup urine disease (MSUD) is a very rare metabolic disorder. It is an inborn error of amino acid metabolism, which classically affects the brain tissue resulting in impairment or death if untreated.

Clinical presentation

Manifests itself in the first few days of life (12-24 hours) with the complex of symptoms which include.

  • poor feeding
  • vomiting
  • ketoacidosis
  • hypoglycemia
  • lethargy
  • seizures
  • a characteristic odour of maple syrup

Pathology

Genetics

It carries an autosomal recessive inheritance 1.

Serology

There is elevated plasma concentrations of branched-chain amino acids (BCAAs) (leucine, isoleucine, and valine) and allo-isoleucine,

Radiographic features 

Neuroimaging (MRI: brain)

MRI may show diffuse swelling of the brain due to extensive oedema of the white matter.

  • DWI: the posterior limbs of the internal capsules and optic radiations and the central corticospinal tracts within the cerebral hemispheres exhibit diffusion restriction, which represents myelin splitting oedema and is believed to be secondary to vacuolating myelinopathy. 
  • MR spectroscopy: single-voxel proton MR spectroscopy may show the presence of branched-chain amino acids (BCAA) and branched-chain alpha-keto acids (BCKA) resonating at 0.9-1.0 ppm, especially during a metabolic crisis 1-2

The structures in the posterior fossa exhibit prominent changes in signal intensity, swelling, and diffusion restriction of the already myelinated brain areas, such as the posterior brainstem tracks and the central cerebellar white matter.


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Inborn errors of metabolism

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