What are the key clinical features to consider when diagnosing Lyme disease in a patient with a recent tick bite?

When diagnosing Lyme disease in a patient with a recent tick bite, the key clinical feature to consider is the presence of erythema migrans ¹. This is a red rash that typically increases in size and may sometimes have a central clearing ¹. It is usually not itchy, hot, or painful ¹. The rash usually becomes visible 1 to 4 weeks after a tick bite, but can appear from 3 days to 3 months, and lasts for several weeks ¹. It is typically located at the site of the tick bite ¹.

It is important to be aware that a rash which is not erythema migrans can develop as a reaction to a tick bite ¹. This type of rash usually develops and recedes within 48 hours of the bite and is more likely to be hot, itchy, or painful ¹. It may be caused by an inflammatory reaction or infection with a common skin pathogen ¹.

If erythema migrans is present, Lyme disease can be diagnosed and treated without laboratory testing ¹,².

In people without erythema migrans, consider the possibility of Lyme disease if they present with several of the following symptoms, as Lyme disease is a possible but uncommon cause ¹:

• Fever and sweats ¹
• Swollen glands ¹
• Malaise ¹
• Fatigue ¹
• Neck pain or stiffness ¹
• Migratory joint or muscle aches and pain ¹
• Cognitive impairment (e.g., memory problems, difficulty concentrating) ¹
• Headache ¹
• Paraesthesia ¹

Also, consider Lyme disease in people presenting with symptoms and signs relating to one or more organ systems (focal symptoms), as it is a possible but uncommon cause of ¹:

• Neurological symptoms, such as facial palsy, other unexplained cranial nerve palsies, meningitis, mononeuritis multiplex, or other unexplained radiculopathy; or rarely encephalitis, neuropsychiatric presentations, or unexplained white matter changes on brain imaging ¹
• Inflammatory arthritis affecting one or more joints that may be fluctuating and migratory ¹
• Cardiac problems, such as heart block or pericarditis ¹
• Eye symptoms, such as uveitis or keratitis ¹
• Skin rashes such as acrodermatitis chronica atrophicans or lymphocytoma ¹

When assessing, explore how long the person has had symptoms and their history of possible tick exposure, including activities that might have exposed them to ticks or travel to highly prevalent areas ¹. However, do not rule out Lyme disease if there is no clear history of tick exposure ¹. Do not diagnose Lyme disease in people without symptoms, even if they have had a tick bite ¹.