Acute motor axonal neuropathy

Acute Motor Axonal Neuropathy (AMAN) is a subtype of Guillain-Barré syndrome (GBS), a rare neurological disorder that affects the peripheral nerves. AMAN specifically targets the motor nerves, leading to muscle weakness and paralysis.

Etiology

The exact cause of AMAN is unknown, but it is often preceded by an infection, such as Campylobacter jejuni, a bacterium commonly associated with food poisoning. Other infections, including Epstein-Barr virus, Cytomegalovirus, and Zika virus, have also been linked to AMAN.

Pathophysiology

In AMAN, the body's immune system mistakenly attacks the axons of motor nerves. This is thought to occur due to molecular mimicry, where the immune system confuses components of the nerves with foreign pathogens. The attack on the axons leads to a rapid onset of muscle weakness and paralysis.

Clinical Presentation

Patients with AMAN typically present with rapidly progressive muscle weakness, often starting in the legs and progressing to the arms. This can lead to difficulty walking, loss of reflexes, and in severe cases, respiratory failure. Sensory symptoms are typically absent or mild, as sensory nerves are not affected in AMAN.

Diagnosis

Diagnosis of AMAN is based on clinical presentation, nerve conduction studies, and cerebrospinal fluid analysis. Nerve conduction studies in AMAN typically show reduced motor nerve conduction velocities and compound muscle action potentials, while sensory nerve conduction is normal. Cerebrospinal fluid analysis often shows albuminocytologic dissociation, a characteristic finding in GBS.

Treatment

Treatment for AMAN is primarily supportive, including physical therapy and respiratory support if needed. Immunomodulatory treatments, such as intravenous immunoglobulin (IVIG) and plasma exchange, are also used to reduce the severity and duration of the disease.

Prognosis

The prognosis of AMAN is generally good, with most patients achieving near-complete recovery. However, the recovery process can be slow, often taking several months to years. Severe cases can result in permanent disability or death, usually due to respiratory failure.