1 |
P a g e
Definition
Tetanus is an acute disease manifested by skeletal muscle spasm and autonomic nervous
system disturbance. It is caused by a powerful neurotoxin produced by the bacterium
Clostridium tetani and is completely preventable by vaccination.
C. Tetani is an anaerobic, gram-positive, slender motile bacillus. The vegetative form
produces tetanospasmin, a protein neurotoxin including a heavy chain that binds neuronal
cells and a light chain that blocks release of neurotransmitters.
Tetanus is most common in warm climates and in highly cultivated rural areas. The greatest
problem occurs in resource-limited countries because of poor immunization standards and
unhygienic practices. An example is the practice of dressing the umbilical stump with animal
dung or “dusting powder,” a local dried clay sold for cosmetic purposes, after childbirth by
unimmunized mothers.
Pathobiology
Clinical tetanus requires a source of the organism, local tissue conditions that promote toxin
production. In circumstances unfavourable to the growth of the organism, spores are
formed and these may remain dormant for years in the soil. Spores germinate and bacilli
multiply only in the anaerobic conditions which occur in areas of tissue necrosis or if the
oxygen tension is low as a result of the presence of other organisms, particularly aerobic
ones. The bacilli remain localised but produce an exotoxin with an affinity for motor nerve
endings and motor nerve cells.
Tetanospasmin binds the peripheral nerve terminals and is then carried intra-axonally within
membrane-bound vesicles to spinal neurons. On reaching the perikarya of the motor
neurons, the light chain passes to the presynaptic terminals, where it blocks the release of
neurotransmitters, including glycine, which is the neurotransmitter used by group 1A
inhibitory afferent motor neurons. Loss of the inhibitory influence results in unrestrained
firing with sustained muscular contraction. In severe cases, involvement of the sympathetic
chain causes autonomic dysfunction. Binding of the toxin is irreversible, so recovery requires
the generation of new axon terminals.
Clinical Manifestations
Forms of tetanus include generalized, localized, cephalic, and neonatal.
Generalized tetanus
: which is the most common form of tetanus, accounts for 85 to 90% of
reported cases in the United States.
The usual incubation period is 7 to 21 days, depending largely on the distance of the site of
injury from the central nervous system. The “onset period” refers to the time from the first
clinical symptoms of tetanus to the first generalized spasm. An incubation period of less
2 |
P a g e
than 9 days and an onset period of less than 48 hours appear to be associated with more
severe symptoms.
The most important early symptom is trismus-spasm of the masseter muscles, which causes
difficulty in opening the mouth and in masticating; hence the name 'lockjaw'. Lockjaw in
tetanus is painless.
In tetanus, the tonic rigidity spreads to involve the muscles of the face, neck and trunk.
Contraction of the frontalis and the muscles at the angles of the mouth leads to the so-called
'risussardonicus'. There is rigidity of the muscles at the neck and trunk of varying degree.
The back is usually slightly arched ('opisthotonus') and there is a board-like abdominal wall.
In the more severe cases, violent spasms lasting for a few seconds to 3-4 minutes occur
spontaneously, or may be induced by stimuli such as moving the patient or noise. These
convulsions are painful, They gradually increase in frequency and severity for about 1 week
and the patient may die from exhaustion, asphyxia or aspiration pneumonia. In less severe
illness, convulsions may not commence for about a week after the first sign of rigidity, and in
very mild infections they may never appear. Autonomic disturbance is maximal during the
second week of severe tetanus, and death due to cardiovascular events becomes the major
risk. Blood pressure is usually labile, with rapid fluctuations from high to low accompanied
by tachycardia.
Localized tetanus
which refers to involvement of the extremity from a contaminated wound, shows
considerable variation in severity. In mild cases, patients may simply have weakness of the
involved extremity, presumably limited by partial immunity. In more severe cases, there are
intense, painful spasms that usually progress to generalized tetanus. This relatively unusual
form of tetanus has an excellent prognosis for survival.
Cephalic tetanus
Generally follows a head injury or occurs with C. tetani infection of the middle ear. Clinical
symptoms consist of isolated or combined dysfunction of the cranial motor nerves, most
frequently the seventh cranial nerve. This dysfunction may remain localized or progress to
generalized tetanus. Cephalic tetanus is a relatively unusual form of tetanus, but the
incubation period is only 1 or 2 days, and the prognosis for survival is usually poor.
Tetanus neonatorum
Which refers to generalized tetanus resulting from C. tetani infection in neonates, occurs
primarily in underdeveloped countries, where it accounts for up to half of all neonatal
deaths. The usual cause is the use of animal dung or “dusting powder” to dress the umbilical
cord in newborns of unimmunized mothers. The usual incubation period after birth is 3 to 10
days, and it is sometimes referred to as “disease of the seventh day,” reflecting the average
3 |
P a g e
incubation period. The child typically shows irritability, facial grimacing, and severe spasms
with touch. The mortality rate exceeds 70%.
Diagnosis
The diagnosis of tetanus is usually based on clinical observations. The causative agent C.
tetani, is infrequently recovered with culture of the wound.
The few conditions that mimic generalized tetanus include strychnine poisoning and
dystonic reactions to antidopaminergic drugs. Strychnine levels in blood and urine establish
the diagnosis. Dystonic reactions may resemble tetanus and are distinguished by rapid
response to anticholinergic agents.
Treatment
Patients with tetanus require intensive care with particular attention to respiratory support,
treatment with benzodiazepines, autonomic nervous system support, passive and active
immunization, surgical débridement, and antibiotics directed against C.tetani.. The severity
of disease may be reduced by partial immunity, so some patients have mild disease with
minimal mortality, whereas others have mortality rates as high as 60% despite expert care.
General measures:
Maintain hydration and nutrition.
Treat secondary infections.
Prevent further toxin production:
Débridement of wound
Metronidazole (400 mg rectally or 500 mg IV every 6 h for 7 days) is the preferred antibiotic.
An alternative is penicillin (100,000–200,000 IU/kg per day),.
Control spasms:
Nurse in a quiet room.
Avoid unnecessary stimuli.
I.v. diazepam-if spasms continue, paralyze patient and ventilate.
Passive Immunization
Antitoxin should be given early in an attempt to deactivate any circulating tetanus toxin and
prevent its uptake into the nervous system. Two preparations are available: human tetanus
immune globulin (TIG) and equine antitoxin. TIG is the preparation of choice as it is less
likely to be associated with anaphylactic reactions. there is evidence that intrathecal
administration of TIG inhibits disease progression and leads to a better outcome.
4 |
P a g e
Active Immunization
The standard three-dose schedule of immunization with tetanus toxoid should be given at
an injection site separate from that used for immunoglobulin.
Autonomic Nervous System Dysfunction
This complication generally reflects excessive catecholamine release and is usually treated
with labetalol (0.25 to 1.0 mg/min) for blood pressure control. Other treatments of
hypertension include morphine by continuous infusion, magnesium sulfate infusion, or
epidural blockade of the renal nerves. Hypotension may require norepinephrine infusion.
Bradycardia may require a pacemaker.
Prevention
Tetanus is a disease of medical neglect. Immunization is virtually 100% effective, so nearly
all cases of tetanus occur in unimmunized or inadequately immunized individuals.
Prevention of tetanus after injury requires appropriate wound management, assurance of
adequate immunity, and consideration of antibiotic prophylaxis. The aim of surgery is to
eliminate necrotic tissue, purulent collections, and foreign bodies that promote the
environmental conditions necessary for spore germination. Passive immunization with
tetanus immune globulin (TIG) is recommended only for “tetanus-prone” wounds in patients
with inadequate or unknown primary immunization status. Antimicrobial agents such as
penicillin, erythromycin, or metronidazole may be given to inhibit replication of the
vegetative forms ofC.tetani but immunization and wound cleansing are considered more
important.
Prognosis
The overall mortality rate for generalized tetanus is 20 to 25%, even in modern medical
facilities with extensive resources. Patients with moderate or severe generalized tetanus
generally require treatment for 3 to 6 weeks. The highest mortality rates are at the extremes
of age. The most frequent cause of death is pneumonia. Patients who recover usually
recover completely.