Discussion

The patient reported his last Tdap was 12 years prior. Tetanus occurs when spores of Clostridium tetani, an obligate anaerobe normally present in the gut of mammals and widely found in soil, gain access to damaged human tissue. After inoculation, C. tetani produces the metalloprotease tetanus toxin (also known as tetanospasmin). The incubation period of tetanus is approximately eight days but ranges from three to 21 days.¹

After reaching the spinal cord and brainstem within the motor neuron, tetanus toxin is secreted and enters adjacent inhibitory interneurons, where it blocks neurotransmission by its cleaving action on the membrane proteins involved in neuroexocytosis.^2-5 The net effect is inactivation of the inhibitory neurotransmission that normally modulates anterior horn cells and muscle contraction. This loss of inhibition of anterior horn cells and autonomic neurons results in increased muscle tone, painful spasms, and widespread autonomic instability.

The most common and severe clinical form of tetanus is generalized tetanus. The presenting symptom in more than 80 percent of such patients is trismus (lockjaw) but they may present with tonic and periodic spastic muscular contraction such as stiff neck, opisthotonos, risus sardonicus (sardonic smile), a board-like rigid abdomen, periods of apnea and/or upper airway obstruction due to vise-like contraction of the thoracic muscles and/or glottal or pharyngeal muscle contraction, and dysphagia.

Patients with generalized tetanus typically have symptoms of autonomic overactivity that may manifest as profuse sweating, tachycardia, cardiac arrhythmias, labile blood pressure, and fever.

Modern Management of an Ancient Disease

Tetanus-toxin-induced effects are long-lasting (up to four to six weeks) because recovery is believed to require the growth of new axonal nerve terminals.

The recommended treatment for tetanus is:

1. Human tetanus immune globulin is the antitoxin of choice to neutralize unbound toxin. The Centers for Disease Control and Prevention recommends a single dose of 500 units intramuscularly (IM).^1,6
2. Since tetanus does not confer immunity following recovery from acute illness, all patients with tetanus should receive active immunization with a full series of tetanus- and diphtheria-toxoid-containing vaccines, immediately upon diagnosis. Such vaccines should be administered at a different site than tetanus immune globulin.
3. Metronidazole (500 mg intravenously [IV] every six to eight hours) is the preferred treatment for tetanus, but penicillin G (2 to 4 million units IV every four to six hours) is a safe and effective alternative.⁸ Treatment duration of seven to 10 days is recommended.
4. In patients with severe tetanus, the mainstay treatment is additional supportive care as needed. This may include mechanical ventilation and benzodiazepines as needed for spasticity.

Accidental or intentional strychnine poisoning may produce a clinical syndrome similar to tetanus and should be strongly considered in a patient who is fully vaccinated or has no obvious wounds. Strychnine was first used as a rodenticide in Germany in the early 16th century. Although rare, most strychnine poisonings today result from the adulteration of street drugs (e.g., cocaine, heroin) as well as from small amounts found in herbal medications and homeopathic remedies.⁷