How is Guillain-Barre syndrome (GBS) diagnosed?
GBS is called a syndrome rather than a disease because it is not clear that a specific disease-causing agent is involved. A syndrome is a medical condition characterized by a collection of symptoms (what the affected person feels) and signs (what a health care provider can observe or measure). The signs and symptoms of GBS can be quite varied, so, on rare occasions, it may be difficult to diagnose in its earliest stages.
Several disorders have symptoms similar to those found in GBS. Collectively, the signs and symptoms form a certain pattern that helps to differentiate GBS from other disorders. For example, if the symptoms appear on both sides of the body (most common in GBS) and symptoms appear rapidly (in other disorders, muscle weakness may progress over months rather than days or weeks), it is more likely to be GBS. In addition, reflexes such as knee jerks are usually lost. Because the signals traveling along the nerve are slower, a nerve conduction velocity test can give clues to aid in the diagnosis. The cerebrospinal fluid that bathes the spinal cord and brain contains more protein than usual in GBS (Levin, 2004). Therefore, a spinal tap (a procedure in which the doctor inserts a needle into the patient’s lower back to draw cerebrospinal fluid from the spinal column) may need to be performed.
The two most common forms can be differentiated with specific tests. AMAN is diagnosed when nerve conduction studies show a reduction of compound muscle action potential without significant conduction slowing. In the AIDP form, immune system reactions result in demyelination. It is diagnosed when nerve conduction studies show slowing of nerve conduction suggestive of demyelination in two or more motor nerves.