how can it be diagnosed?
It depends on findings such as rapid development of muscle paralysis, absent reflexes, absence of fever, and absence of a likely cause.
Guillain–Barré syndrome
The diagnosis of Guillain–Barré syndrome depends on findings such as rapid development of muscle paralysis, absent reflexes, absence of fever, and absence of a likely cause. 
where do the cranial nerves branch off the brain The terminal nerves; olfactory nerves and optic nerves emerge from the cerebrum, and the remaining ten pairs arise from the brainstem, which is the lower part of the brain. what do they do? They relay information between the brain and parts of the body. do they have a nucleus? All cranial nerves have a nucleus. With the exception of the olfactory nerve and optic nerve, all the nuclei are present in the brainstem. what is this first type of nerve? It is typically considered the first cranial nerve, or simply CN I, that contains sensory nerve fibers relating to the sense of smell. and what about the second type? It is known as cranial nerve II, or simply as CN II, a paired cranial nerve that transmits visual information from the retina to the brain. what ailments can cn ii suffer from? Damage to the optic nerve typically causes permanent and potentially severe loss of vision, as well as an abnormal pupillary reflex. what is its form or shape like? It is derived from an out-pouching of the diencephalon (optic stalks), the fibers of the optic nerve are covered with myelin. how is it related to the guillain disease? They are not affected by it. what part of the body is affected by this disease? Beginning in the feet and hands, often spreading to the arms and upper body. what are its signs? Upper respiratory tract infection or diarrhea infection in the 3–6 weeks prior to the onset of the neurological symptoms.
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Guillain–Barré syndrome [SEP] Diagnosis
The diagnosis of Guillain–Barré syndrome depends on findings such as rapid development of muscle paralysis, absent reflexes, absence of fever, and absence of a likely cause. Cerebrospinal fluid analysis (through a lumbar spinal puncture) and nerve conduction studies are supportive investigations commonly performed in the diagnosis of GBS. Testing for antiganglioside antibodies is often performed, but their contribution to diagnosis is usually limited. Blood tests are generally performed to exclude the possibility of another cause for weakness, such as a low level of potassium in the blood. An abnormally low level of sodium in the blood is often encountered in Guillain–Barré syndrome.