Pictorial Case Study: Insect bite

The case: It was half-term and my grandchildren were in the New Forest for a holiday. They had enjoyed exploring the woods and taking walks over the moors. Later, at home, there were screams when a bulging tick was noticed clinging to the back of the thigh of the 14-year-old. A spreading, slightly itchy, erythematous rash had also appeared around the tick.

After a tick bite, an asymptomatic or slightly itchy erythematous rash appears
After a tick bite, an asymptomatic or slightly itchy erythematous rash appears

Diagnosis and management
The rash surrounding the tick was suggestive of Lyme disease. The tick was carefully removed, by holding tweezers close to the skin and gently pulling it out. The tick was kept in a small bottle to take as evidence when visiting the GP the next day. In view of the history and rash, the GP prescribed a single dose of 200mg doxycycline to shorten the duration of the rash and prevent further complications.

Lyme disease is transmitted to humans after a bite from a tick infected by Borrelia burgdorferi. The tick acquires the infection when feeding on infected animals, particularly mice. Soon after the tick bite, an asymptomatic or slightly itchy erythematous rash appears.

If left untreated, the rash may last two to three weeks. Lyme disease may also be associated with fever and myalgia and further complications occur in patients who are not treated. Stage two disease can present with intermittent inflammatory arthritis, cranial nerve palsies, chronic neuropathy and chronic fatigue.

Early treatment (within 72 hours of bite) is doxycycline 200mg, regardless of whether there is a rash. Late complications should be treated with a 30-day course of oral doxycycline. IV antibiotics should be given where there is neuropathy or encephalitis.

Possible Differential diagnoses

  • Fibromyalgia
  • Rheumatoid or reactive arthritis
  • Systemic lupus erythematosus
  • Aseptic meningitis
  • Bell's palsy

Differential diagnosis
Fibromyalgia

  • May occur in either sex but most common in women between aged 20-50 years.
  • Often occurs after viral illness or accident.
  • Chronic problem of pain and fatigue.
  • Investigations may help to exclude other conditions but will not confirm fibromyalgia.
  • Exercises should be introduced slowly. Advise patients of counselling and support.
  • Treatment includes pregabalin and duloxetine.
  • Severe problems may require referral.

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