Lyme disease: Clinical sciences

Lyme disease is an infectious disease caused by the spirochete Borrelia Burgdorferi. It’s most commonly transmitted via the Ixodes Scapularis deer tick in Lyme-endemic areas like the Northeastern and Midwestern United States. After a tick bite, spirochetes replicate at the site of infection, causing symptoms ranging from an isolated rash to neurological, cardiac, and musculoskeletal involvement. Depending on the timing of infection and clinical presentation, Lyme disease is classified into early localized, early disseminated, and late Lyme disease.

If your patient presents with chief concerns suggesting Lyme disease, your first step is to perform a focused history and physical. Let’s start with early localized Lyme disease! Your patient will report a known tick bite or exposure to a Lyme-endemic area in the last 4 weeks. Other symptoms may include fever, a non-painful rash, and non-specific symptoms, such as headache, myalgias, and fatigue. On physical exam, you’ll see a single skin lesion called erythema migrans, which looks like a red, warm, and swollen rash with central clearing that may resemble a bullseye! With these findings, diagnose early Lyme disease, and treat empirically with oral doxycycline for 10 days.

Here’s a high-yield fact! Erythema migrans is found in 80% Lyme disease cases, most commonly appearing in the groin, axilla, and thighs. If a patient’s rash does not have typical characteristics of erythema migrans, you can delay treatment until laboratory testing confirms the presence of Borrelia antibodies. Early in the course of infection, initial testing can be negative, so if clinical suspicion remains high, consider retesting in 2 to 3 weeks, which is the time required for the immune system to produce antibodies.

And now a clinical pearl! Prophylactic treatment with a single 200-milligram dose of doxycycline orally is recommended after a tick bite within 72 hours of tick removal. However, you should give prophylactic treatment only if the tick is an Ixodes species, the tick bite occurred in a highly endemic area, the tick was attached for at least 36 hours, and it’s been less than 72 hours from tick removal. If all of these criteria aren’t met, just observe, and treat if the patient develops erythema migrans.

Now, if patients don’t get treated during the early localized stage, they can progress to early disseminated Lyme disease. These individuals usually report a history of a known tick bite or exposure to a Lyme-endemic area in the last 12 weeks. Additionally, early disseminated Lyme can affect a variety of organs and body systems, so your patient may report a range of symptoms. These may include diffuse cutaneous involvement; cardiac manifestations like chest pain or bradycardia; or neurologic symptoms, such as cranial nerve palsies or paresthesias.