X-rays, electrocardiograms, and common tests of the blood and urine are often helpful to diagnose neurological syndromes, but there are also specialized tests that may be useful for certain situations. Imaging beyond plain film x-rays may show certain abnormalities, particularly computed tomography and magnetic resonance imaging of the central nervous system. Both of these tests can show different aspects of abnormalities of the tissue of the central nervous system, as well as nearby bony and soft tissue structures. Administration of contrast agents can show even more details of abnormalities of these tissue, as well as other abnormalities of blood vessels.
Nerve conduction studies and electromyography are electrical tests that may show dysfunction of parts of the peripheral nervous system or skeletal muscle. Nerve conduction studies involve administering electricity to certain parts of nerves, and recording the electrical responses of other parts of nerves, or of muscles. Electromyography involves insertion of needle electrodes into skeletal muscles to assess their electrical activity on insertion, at rest, and with increasing strength of contraction. With polyneuropathy, this test may show diffuse abnormalities. With focal nerve or spinal nerve dysfunction, this test usually shows abnormalities at the area of dysfunction. Abnormalities may also be seen in axons distal to the lesion if they have degenerated, which often happens if distal parts of axons are cut off from their somas. The patterns of abnormalities found on nerve conduction studies and electromyography often help locate dysfunction in the peripheral nervous system or in skeletal muscle, and may quantify the severity the lesion as well.
Electroencephalography is an electrical test that may show abnormalities of parts of the cerebrum, particularly the cerebral cortex. The electroencephalogram uses electrodes on the scalp to record the average of the electrical activity of many neurons in the part of the cerebral cortex under the electrode. In a normal awake adult, the complexity of information flowing through the vast number of neurons in the cerebral cortex mostly cancels out the voltage changes that reach the electrodes, which produces, for the most part, a low voltage, somewhat random-appearing series of waveforms. There are also several types of more organized-appearing waveforms that may appear during normal wakefulness, and different waveforms that characterize the different stages of normal sleep. Seizures involve abnormally increased and synchronous neuronal firing, primarily in the cerebral cortex, which may produce abnormal higher voltage or rhythmic waveforms on the electroencephalogram.
Lumbar puncture, also called “spinal tap”, uses a needle to access the cerebrospinal fluid in the low part of the spine. This can provide useful information about the cerebrospinal fluid, and also the interstitial fluid of the central nervous system because there is a relatively leaky barrier between these fluid compartments. Cerebrospinal fluid can be tested for the presence of blood, as well as many markers of inflammation, infection, and other abnormalities. Some neurological disorders may require biopsy for diagnosis. Biopsy of the brain may be needed to diagnose certain disorders, particularly tumors in the brain. Some unusual causes of neuropathy need a biopsy of a small nerve, and many kinds of myopathy require skeletal muscle biopsy for diagnosis.