Symptoms vary greatly in severity from so mild that medical attention is not sought, to severe causing almost total paralysis, which may include respiratory failure. The common initial symptoms are numbness and tingling in the legs. Back pain is a major symptom in about one third of patients. The sensory symptoms are soon followed by ascending weakness in the legs and arms. Other nerves, such as those controlling the eyes, are affected in over half the cases.
Reflexes are usually absent or greatly reduced.
Progression of the symptoms may continue for up to four weeks. Recovery is often slow, lasting 6 months to two years. There is no single reliable diagnostic test. A variety of tests are often performed, including nerve conduction studies and tests to measure muscle weakness and sensory changes. Diagnosis is usually made based upon clinical symptoms and exclusion of other possible causes of the ascending paralysis.