Acute Inflammatory Demyelinating Polyneuropathy (AIDP) is a serious, rapidly progressing autoimmune disorder. The body’s defense mechanisms mistakenly target healthy tissue, specifically the peripheral nerves outside of the brain and spinal cord. This misplaced immune attack damages the protective coating of these nerves, disrupting the transmission of signals between the brain and the rest of the body. AIDP demands immediate medical attention due to its potential for swift progression and severe complications.
Defining Acute Inflammatory Demyelinating Polyneuropathy
The condition’s name describes its nature and progression. “Acute” refers to the rapid onset, with symptoms peaking within four weeks or less. “Inflammatory” signifies an immune response where white blood cells and antibodies infiltrate nerve tissues. This immune attack is “Demyelinating” because it targets the myelin sheath, the fatty layer that insulates nerve fibers and allows for fast signal transmission. Damage to this insulation slows or blocks electrical signals, causing neurological symptoms.
“Polyneuropathy” indicates the disorder affects multiple peripheral nerves extending from the spinal cord. AIDP is the most common subtype of Guillain-Barré Syndrome (GBS), accounting for approximately 90% of cases. Unlike other GBS variants, AIDP specifically involves damage to the myelin sheath rather than the nerve axon itself.
Recognizing the Clinical Signs
The typical presentation of AIDP begins with sensory changes, often described as tingling or “pins and needles” (paresthesia), usually starting in the feet and hands. This is followed by the hallmark sign: progressive muscle weakness. This weakness is typically symmetrical and follows an ascending pattern, starting in the legs and moving upward toward the arms and torso. The progression is swift, often impeding walking within two weeks of onset. A loss or significant reduction of deep tendon reflexes is also a consistent finding in affected limbs.
In up to 30% of cases, weakness may involve the muscles necessary for breathing, necessitating mechanical ventilation. This represents a medical emergency. Involvement of cranial nerves can lead to difficulties with facial movement, speech, and swallowing. Many patients also experience autonomic dysfunction, resulting in unpredictable fluctuations in heart rate and blood pressure that require careful monitoring.
Identifying Triggers and Underlying Causes
AIDP is understood to be a post-infectious autoimmune response, meaning neurological symptoms follow a recent infection. The immune system reacts to a foreign invader, such as a bacterium or virus, and mistakenly attacks components of the peripheral nerves. This mechanism, called molecular mimicry, occurs when the immune system confuses a part of the nerve structure with a component of the original infectious agent.
The most frequent trigger is infection with the bacterium Campylobacter jejuni, which typically causes gastrointestinal illness. Other common antecedent events include respiratory infections caused by viruses like Cytomegalovirus (CMV), Epstein-Barr virus, and influenza. AIDP onset has also been reported following surgery, trauma, or, rarely, certain vaccinations. The preceding infection usually occurs one to six weeks before neurological symptoms begin. While a trigger is identified in about two-thirds of cases, the exact cause is not fully understood in every patient.
Establishing a Diagnosis and Treatment Protocols
Diagnosing AIDP relies on clinical presentation, laboratory tests, and electrophysiological studies. Evaluation often begins with a lumbar puncture (spinal tap) to analyze the cerebrospinal fluid (CSF). A classic finding is “albuminocytologic dissociation,” involving an abnormally high protein level in the CSF but a normal white blood cell count.
Nerve conduction studies (NCS) and electromyography (EMG) confirm the diagnosis and characterize the nerve injury. These electrodiagnostic tests measure the speed and strength of electrical signals in the nerves and muscles. AIDP results typically show evidence of demyelination, such as slowed nerve conduction velocities or conduction block.
Treatment is time-sensitive and focuses on mitigating the immune attack to limit nerve damage. The two primary disease-modifying treatments, which are equally effective, are Intravenous Immunoglobulin (IVIg) and Plasma Exchange (Plasmapheresis).
IVIg involves administering high doses of healthy donor antibodies over several days to neutralize autoantibodies and reduce inflammation. Plasma Exchange physically removes the blood’s liquid component (plasma) to filter out circulating antibodies attacking the nerves. The plasma is then replaced with a substitute or donor plasma. Both treatments aim to shorten the duration of nerve damage and hasten recovery.
Expected Recovery and Long-Term Outlook
AIDP is often a monophasic illness, meaning it typically occurs only once, and most patients experience significant recovery. Approximately 70% to 80% of individuals who receive prompt treatment achieve a full or near-full recovery of motor function. Recovery is slow, often taking several months to a year or more, as the body repairs the damaged myelin sheath. Improvement usually begins after symptoms have peaked and plateaued, typically within the first four weeks. Physical and occupational therapy play a significant role in the recovery phase, helping patients regain strength, mobility, and functional independence.
While the outlook is generally positive, about 10% to 15% of patients may be left with residual weakness, fatigue, or chronic nerve pain. Factors associated with a slower or less complete recovery include advanced age, the need for mechanical ventilation, and rapid disease progression. Death is uncommon, occurring in an estimated 2% to 6% of cases, usually due to complications like respiratory failure or autonomic instability.