Diagnosis

To diagnose paraneoplastic syndrome of the nervous system, your doctor will need to conduct a physical exam and order blood tests. He or she may also need to request a spinal tap or imaging tests.

Because paraneoplastic syndromes of the nervous system are associated with cancer, your doctor may also perform certain cancer screening tests based on your age.

Clinical exam

Your doctor or a neurologist will conduct a general physical, as well as a neurological exam. He or she will ask you questions and conduct simple tests in the office to judge:

• Reflexes
• Muscle strength
• Muscle tone
• Sense of touch
• Vision and hearing
• Coordination
• Balance
• Mood
• Memory

Laboratory tests

Laboratory tests will likely include:

• Blood tests. You may have blood drawn for a number of laboratory tests, including tests to identify antibodies commonly associated with paraneoplastic syndromes. Other tests may attempt to identify an infection, a hormone disorder or a disorder in processing nutrients (metabolic disorder) that could be causing your symptoms.

• Spinal tap (lumbar puncture). You may undergo a lumbar puncture to obtain a sample of cerebrospinal fluid (CSF) — the fluid that cushions your brain and spinal cord. A neurologist or specially trained nurse inserts a needle into your lower spine to remove a small amount of CSF for laboratory analysis.

  Sometimes, paraneoplastic antibodies may be found in CSF when they can't be seen in your blood. If these antibodies are found in both your CSF and your blood, it provides strong evidence that your nervous system symptoms are caused by a specific form of activation of the immune system.

Imaging tests

Imaging tests are used to find a tumor that may be the underlying problem or to identify other factors causing your neurological symptoms. One or more of the following tests may be used:

• Computerized tomography (CT) is a specialized X-ray technology that produces thin, cross-sectional images of tissues.
• Magnetic resonance imaging (MRI) uses a magnetic field and radio waves to create detailed cross-sectional or 3D images of your body's tissue.
• Positron emission tomography (PET) uses radioactive compounds injected into your bloodstream to produce cross-sectional or 3D images of the body. PET scans can be used to identify tumors, measure metabolism in tissues, show blood flow and locate brain abnormalities related to seizures.
• PET plus CT, a combination of PET and CT, may increase the detection rate of small cancers, common in people who have paraneoplastic neurological disorders.

If no malignant tumor is located or no other cause identified, the problem may still be related to a tumor that is too small to find. The tumor may be causing a powerful response from the immune system that is keeping it very small. You'll likely have follow-up imaging tests every three to six months until a cause for the neurological disorder is identified.