There are many ways to diagnose which disorder may be causing a neurological syndrome, but the following approach may be the most efficient. The first step is to locate the lesion based on the syndrome (symptoms and signs), because different types of pathology (disorders or diseases) tend to cause focal or diffuse dysfunction of different parts of the nervous system. The second step is to further shorten the list of likely types of pathology by factoring in the syndrome time course, particularly the speed of onset or progression. The third step is to consider risk factors that might increase the likelihood of certain specific disorders. These steps create a list of likely disorders, ranked by probability, which is called the differential diagnosis. This list determines the best strategy for tests and treatments, if any are needed. This approach is the same as that used for syndromes caused by dysfunction of the other systems of the body, but the localization step tends to be more involved because of the size and complexity of the nervous system. There are some fairly arbitrary divisions of which disorders are usually managed by neurologists versus psychiatrists or some other specialties, but all of these disorders are first seen by primary or emergency care providers, and referral to a specialist is only sometimes necessary.
The types of pathology that may affect the nervous system can be categorized in different ways; one system could be: genetic, idiopathic, vascular, epileptic, immune, mechanical, metabolic, infectious, neoplastic, environmental, nutritional, and toxic (with the less-than-ideal acronym GIVE IMMINENT). Most neurological disorders fall into one of these types of pathologies, although some may have aspects of more than one.
Routine tests, such as x-rays, electrocardiograms, or common tests of the blood and urine are often helpful to diagnose the cause of neurological syndromes, but there are also specialized tests that may be useful for certain situations. Imaging tests, or scans, beyond plain x-rays may show certain abnormalities, particularly scans of central nervous system tissues, blood vessels, and surrounding structures made with computed tomography and magnetic resonance imaging. Nerve conduction studies and electromyography are electrical tests that may detect abnormalities of the peripheral nervous system or skeletal muscle. Electroencephalography is an electrical test that may detect certain abnormalities of parts of the brain. Lumbar puncture is a test where a needle withdraws a sample of cerebrospinal fluid, which flows through spaces inside and around the brain and spinal cord; this may detect certain abnormalities of the tissues in or around the nervous system. Biopsy, or removing a small piece of tissue, of a skeletal muscle, a nerve, or the brain may help with diagnosis in some situations.
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Introduction to Neurology 