Stella, seven-year-old, FS, Labrador Retriever

Photo of Stella prior to the onset of any clinical signs.

Presenting Complaint

• abnormal facial expression
• difficulty eating and swallowing (1-day duration)

Photos of Stella on the day of presentation.

Exam

Ears were subjectively lower and pulled back compared to her regular appearance and she had moderate elevation of the nictitating membrane bilaterally – neuro exam otherwise normal.

Bloodwork

Mildly elevated cholesterol, slightly low creatine phosphokinase (CPK), normal total thyroxine was normal.

Differential Diagnosis

Masticatory muscle myositis, myasthenia gravis, oral pain, and tetanus. Strong consideration was given to the latter considering the clinical signs. A presumptive diagnosis of tetanus was assigned.

Photos of Stella on the day of presentation.

Outcome

Stella has a long history of being a hunting dog and had been on a hunting trip ~3-4 weeks prior to the onset of clinical signs. We believe she may have suffered a wound or was otherwise exposed at that time. No external wound was found. Overall, Stella did very well in that the condition was recognized and treatment (with metronidazole) was started prior to an overwhelming and widespread contraction of all of her muscles. Her signs gradually resolved over 2-3 weeks.

Tetanus Disease Summary

Clinical Signs

Signs start 5-10 days after exposure and may persist for up to 3 weeks. Affected animals commonly have rigidity of the limbs, extension of the neck, clenching of the jaw (trismus), a characteristic facial expression (risus sardonicus) and less commonly cardiac arrythmia and seizure.

Pathophysiology

The signs of tetanus are caused by a neurotoxin produced by Clostridium tetani, an obligate anaerobic spore forming Gram-positive bacteria. Spores found in the environment will germinate in response to anaerobic conditions (such as in a deep penetrating wound, or in teething animals) and produce various toxins. The toxins invade peripheral nerves at the axonal terminals and ascend to the spinal cord. The most significant of these toxins (ie. tetanospasmin) blocks inhibitory neurotransmitter release at interneurons in the spinal cord and brain. This results in the inability for muscles to relax.

Diagnosis

A diagnosis of tetanus is usually based on solely on clinical signs. Blood samples for complete blood count (CBC) and biochemistry will often be unhelpful although an elevation in creatine kinase may be noted. A wound may be detected; however, in the majority of cases, one is never found. Isolation (culture) of C. tetani can be attempted but this requires anaerobic conditions and special culture media. Growth is slow and will often take longer than 12 days.

Treatment

Treatment of tetanus may include wound debridement, intravenous antitoxin, sedation/muscle relaxation, antibiotics, and intense nursing care (feeding, maintaining hydration, preventing soiling, etc). Untreated cases are often fatal due to respiratory complications.

Wound debridement followed by topical antiseptics is important to remove any necrotic tissue found and inhibit further bacterial growth.

Antitoxin neutralizes any free or unbound toxin and (if used) should be given as soon as possible after the onset of clinical signs. Unfortunately, intravenous administration of antitoxin is associated with a high prevalence of anaphylaxis.

Muscle relaxants and sedatives are indicated in cases with marked muscle rigidity and hyperexcitability. Diazepam or clorazepate can be used for muscle relaxation and/or seizure activity. Phenothiazine derivatives (e.g., acepromazine) have a sedative effect and a weak anticholinergic action.

Antibiotic therapy is indicated to eliminate vegetative C. tetani organisms and prevent further toxin formation. It is important to realize antibiotics have no effect on toxin that has already bound to the nerves. Penicillin has long been thought to be the drug of choice but a 1985 study found metronidazole to be more effective than penicillins. It suggested dogs receiving metronidazole had an improved response, with a significantly lower mortality rate and a shorter stay in the hospital.

Intense nursing care is important since patients are often hyperthermic, dysphagic, hyperexcitable and prone to dermatitis from urine/fecal soiling. Some cases will require tube feeding if dysphagia is severe. Tracheostomy if laryngeal spasms develop. Physiotherapy is important to improve blood supply to and lymphatic drainage from the rigid muscles. It also helps relax spastic muscles and improve comfort.

Photos of Stella after resolution of clinical signs.

Case Outcome

Stella did very well in that the condition was recognized and treatment (with metronidazole) was started prior to an overwhelming and widespread contraction of all of her muscles. Her signs gradually resolved over 2-3 weeks. In more severe or fulminant cases of tetanus, patients commonly experience malnutrition from the inability to eat, aspiration pneumonia, hyperthermia, and respiratory distress/fatigue due to the inability to effectively use the diaphragm and intercostal muscles.