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Diagnosing NBIA

The diagnosis is usually suspected when brain MRI findings suggest abnormal iron accumulation in the basal ganglia. Although all of us have iron in this area, people with NBIA have extra iron made visible on MRI (magnetic resonance imaging) scans.  Certain views (T2-weighted images) show the iron as dark regions in the brain.  High brain iron is most often seen in the part of the basal ganglia called the globus pallidus and the substantia nigra.

The hallmark clinical manifestations of NBIA relate to the body’s muscle function and feature progressive dystonia (a movement disorder) and dysarthria (problems speaking), spasticity and parkinsonism, a condition marked by tremor, slowness, rigidity (stiff muscles) and poor balance.

Vision also may be affected. The most common conditions are degeneration of the retina and optic atrophy, the permanent loss of some or most of the fibers in the optic nerve. A general loss of brain cells and brain tissue also are frequently observed, conditions called cerebral atrophy and cerebellar atrophy.

Individuals with NBIA share an abnormality in the nerve cells that can only be detected by performing electron microscopy on nerve tissue obtained from a biopsy. Nerve cells have long extensions, called axons that transmit messages from one nerve cell to the next. In NBIA, some axons are swollen with collections of cellular debris or “junk” that should not be there. These swellings are called spheroids, spheroid bodies or axonal spheroids. In most forms of NBIA, spheroids are located only in the nerves of the brain and spinal cord. Therefore, they are usually not detected until after death, from an autopsy. In one form of NBIA, infantile neuroaxonal dystrophy (INAD), however, spheroids are also found in nerves throughout the body and a biopsy can be done on skin, muscle, or other tissue to look for them.  In a few cases of Mitochondrial-membrane Protein-Associated Neurodegeneration (MPAN), spheroids have also been found in peripheral nerves.

Clinical findings and genetic testing can establish the diagnosis of specific forms of NBIA.