Dr. Najjar's key test was the clock test. This test gave concrete evidence that the right hemisphere of Susannah's brain was inflamed. When one side of the brain isn't working properly and the flow of information is obstructed, the visual world becomes lopsided. Susannah's drawing showed that the right hemisphere was compromised, "to say the least". In other words, Susannah's brain did not care what was going on on the left side of its universe. This also explained the numbness that she had experienced on the left side of her body. It also ruled out schizoaffective disorder and postictal psychosis. This simple test lead to a biopsy of Susannah's brain which lead to the discovery of her illness. On page 148, we finally find out what Susannah has: anti-NMDA-receptor encephalitis. 

Dr. Najjar's test was very different than the other test that Susannah went through. She endured a large spectrum of neurology test, including: MRI's, CT's, and spinal taps. Other doctors relied on blood work and running labs. These test results usually came back normal or an elevated level of white blood cells.  

After doing some research on neurological tests, I found that they are "vital tools that help physicians confirm or rule out the presence of a neurological disorder or other medical condition.  A century ago, the only way to make a positive diagnosis for many neurological disorders was by performing an autopsy after a patient had died.  But decades of basic research into the characteristics of disease, and the development of techniques that allow scientists to see inside the living brain and monitor nervous system activity as it occurs, have given doctors powerful and accurate tools to diagnose disease and to test how well a particular therapy may be working. Researchers and physicians use a variety of diagnostic imaging techniques and chemical and metabolic analyses to detect, manage, and treat neurological disease.  Some procedures are performed in specialized settings, conducted to determine the presence of a particular disorder or abnormality.  Many tests that were previously conducted in a hospital are now performed in a physician’s office or at an outpatient testing facility, with little if any risk to the patient.  Depending on the type of procedure, results are either immediate or may take several hours to process. Laboratory screening tests of blood, urine, or other substances are used to help diagnose disease, better understand the disease process, and monitor levels of therapeutic drugs. For example, blood and blood product tests can detect brain and/or spinal cord infection, bone marrow disease, hemorrhage, blood vessel damage, toxins that affect the nervous system, and the presence of antibodies that signal the presence of an autoimmune disease. Blood tests are also used to monitor levels of therapeutic drugs used to treat epilepsy and other neurological disorders. Analysis of the fluid that surrounds the brain and spinal cord can detect meningitis, acute and chronic inflammation, rare infections, and some cases of multiple sclerosis. A neurological examination assesses motor and sensory skills, the functioning of one or more cranial nerves, hearing and speech, vision, coordination and balance, mental status, and changes in mood or behavior, among other abilities. Items including a tuning fork, flashlight, reflex hammer, ophthalmoscope, and needles are used to help diagnose brain tumors, infections such as encephalitis and meningitis, and diseases such as Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and epilepsy. Some tests require the services of a specialist to perform and analyze results. Biopsy involves the removal and examination of a small piece of tissue from the body. Muscle or nerve biopsies are used to diagnose neuromuscular disorders and may also reveal if a person is a carrier of a defective gene that could be passed on to children.  A small sample of muscle or nerve is removed under local anesthetic and studied under a microscope.  The sample may be removed either surgically, through a slit made in the skin, or by needle biopsy, in which a thin hollow needle is inserted through the skin and into the muscle. A small piece of muscle or nerve remains in the hollow needle when it is removed from the body. The biopsy is usually performed at an outpatient testing facility. A brain biopsy, used to determine tumor type, requires surgery to remove a small piece of the brain or tumor.  Performed in a hospital, this operation is riskier than a muscle biopsy and involves a longer recovery period. Brain scans are imaging techniques used to diagnose tumors, blood vessel malformations, or hemorrhage in the brain.  These scans are used to study organ function or injury or disease to tissue or muscle. Types of brain scans include computed tomography, magnetic resonance imaging, and positron emission tomography." (National Institute of Neurological Disorders and Stroke)

As you can see, these test have great value and there are many different kinds. Without them, finding the cause of an illness or making a diagnosis would be near impossible.