Tetanus

Monday, April 2, 2012

Tetanus is an acute infectious disease characterized by rigid spasmodic contraction of several voluntary muscles, specially those of the neck, jaws, and trunk (muscles involved in expanding the chest in breathing). Tetanus is a neurological disorder that results from a decrease of the inhibitory input to alpha motor neurons. It occurs when spores of the soil bacterium Clostridium tetani (also known as Nicolaier's bacillus) invade a poorly oxygenated wound. Proliferation of the bacterium under anaerobic conditions induces it to secrete a neurotoxin that specifically targets inhibitory interneurons in the brainstem and spinal cord. Blockage of neurotransmitter release from these interneurons allows the normal excitatory inputs to dominate control of the alpha motor neurons, and the result is high-frequency action potential firing that causes increased muscle tone and spasms.

Because the toxin attacks interneurons by traveling backward along the axons of alpha motor neurons, muscles with short motor neurons are affected first. Muscles of the head fall into this category, in particular those that move the jaw. Rigid clamping-shut of the jaw occurs, because the muscles that close it are much stronger than those that open it. Appearance of this symptom early in the disease process is the reason for the common name of this condition, lockjaw. Treatment for tetanus includes: (1) antibiotics to kill the bacteria, (2) injecting antibodies that bind the toxin (tetanus immune globulin, or TIG), (3) drugs to relax and/or paralyze spastic muscles, and (4) mechanical ventilation of the lungs, to maintain air flow despite spastic or paralyzed respiratory muscles. With prompt treatment, approximately 90 percent of patients with tetanus make a complete recovery within a few months.