A thorny case of spastic paralysis

Clinical record

A 78‐year‐old man presented to the emergency department with severe left thigh pain. The patient's past medical history included mild asthma, trigeminal neuralgia and glaucoma. At triage, he appeared in obvious pain and was diaphoretic. Examination of his thigh demonstrated small superficial abrasions with surrounding erythema but no features of compartment syndrome. Initial investigations revealed evidence of systemic inflammation, with elevated white cell count (24.6×10⁹ cells/L; reference interval [RI], 4–11×10⁹/L) and C‐reactive protein (23mg/L; RI, <10mg/L). There was also evidence of acute kidney injury complicating rhabdomyolysis, with estimated glomerular filtration rate 43mL/min/1.73m² (RI, >90mL/min/1.73m²) and creatinine kinase 980U/L (RI, 60–285U/L). A computed tomography scan of the left thigh was unremarkable.

Seven hours after his initial presentation, the patient developed trismus and episodes of painful muscular spasms of the jaw, neck and thigh. Collateral history revealed the patient had dysphagia and increasing left thigh pain over the past 24hours. He was noted to be a keen gardener and recalled a recent injury to his right hand. He used proprietary weed killers, denied exposure to strychnine and was not prescribed any medications associated with dystonia or neuroleptic malignant syndrome. Targeted examination revealed a small area of erythema on the right thenar eminence with a subcutaneous foreign body at this site, which may have represented an alternative or concurrent site of inoculation.

A clinical diagnosis of tetanus was made. He had received his full complement of childhood vaccinations but estimated receiving a tetanus booster 20 years prior. Tetanus immunoglobulin and the diphtheria–tetanus–pertussis vaccine were both available on‐site and administered expeditiously. Intravenous metronidazole and benzylpenicillin were commenced following a discussion of the case among senior colleagues. Spasms were managed with intravenous midazolam and fentanyl.

Due to the episodic trismus, the patient underwent intubation for airway protection and was transferred to the intensive care unit, where sedation with intravenous propofol and midazolam was continued. The foreign body in the patient's right hand was removed. The tissue was cultured and grew an anaerobic gram‐positive rod with terminal spores consistent with Clostridium tetani (Box). A tracheostomy was performed one week later, and baclofen was given intrathecally to control ongoing spasms with good effect. At seven weeks, intrathecal baclofen was ceased in favour of oral baclofen, and his tracheostomy was decannulated.

The patient was discharged home following a period of inpatient rehabilitation. Five months after his presentation, the patient is symptom‐free.

Discussion

Tetanus is a clinical syndrome mediated by the tetanospasmin toxin of Clostridium tetani, a strictly anaerobic spore‐forming gram‐positive bacillus that infects contaminated wounds.1 Tetanospasmin enters the circulation via capillaries and lymphatics to reach local nerves endings, where it is endocytosed.1 The irreversible binding of tetanospasmin at central inhibitory neurons blocks acetylcholine release at the neuromuscular junction resulting in inhibition of γ‐aminobutyric acid (GABA) release, with this loss of inhibition manifesting as prolonged, painful spastic paralysis.1 Airway compromise may develop with eventual apnoea and death. In the early stages of tetanus, autonomic symptoms of restlessness, tachycardia and diaphoresis may be present. Our patient's presentation was unusual insofar as his symptoms began with localised tetany of the thigh with subsequent progression to generalised tetanus.

Rates of tetanus have decreased with the introduction of tetanus immunisation and improved perinatal hand hygiene and wound management. The incidence of tetanus in Australia is three to seven cases per year, with a case fatality rate estimated to be 10–24%.2,3 As a vaccine‐preventable illness, tetanus is a notifiable condition on clinical suspicion alone.4 At 78 years old, our patient belongs to the age group at greatest risk of tetanus in Australia, with most cases occurring in older people. More than three‐quarters of people aged over 70 years have waning or absent levels of tetanus antibody.5 This contrasts with low and middle‐income countries, where most cases are maternal or neonatal.3

Tetanus remains a clinical diagnosis. Microscopy and culture are insensitive, with C. tetani isolated in 20–30% of cases.6 Clinical suspicion should be communicated to the microbiology laboratory and culture should include incubation in anaerobic conditions. The absence of protective antibodies to tetanus toxin may help support a diagnosis of tetanus, but seropositivity does not exclude a diagnosis of tetanus.6

Supportive care remains the mainstay of treatment. This includes securing the airway, establishing mechanical ventilation, ionotropic support to offset autonomic dysfunction and the use of benzodiazepines and propofol to ease tetany.7 Administration of tetanus immunoglobulin should be pursued as soon as the diagnosis of tetanus is considered in order to neutralise the unbound tetanus toxin.7 Given tetanus immunoglobulin does not confer long term immunity and the clinical disease is non‐immunising, vaccination with toxoid vaccine should also be undertaken simultaneously and administered in a different site to tetanus immunoglobulin.8 Metronidazole or penicillin should be administered to eliminate any remaining spores in conjunction with debridement of any suspected area of inoculation or infected wounds.7 Studies of antibiotics in tetanus are limited, and dual therapy has not been assessed.

Tetanus is a rare and life‐threatening illness that causes progressive rigid paralysis and death. Prompt recognition of the clinical manifestations of tetanus is critical to improving survival rates. Vaccination remains important in preventing cases of tetanus, with booster doses recommended every ten years.

Box – Gram stain of cultured organism showing gram‐positive rods with terminal spores (arrow)*

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* Clostridium tetani may easily decolourise and begin to appear gram‐negative (as in this image), especially when performed on older colonies growing on agar.