In what percentage of Lyme disease cases does the Erythema migrans (EM) or bulls eye rash NOT occur?

Erythema migrans, commonly known as the "bull's eye rash," is a characteristic skin lesion that typically appears in cases of Lyme disease, particularly during the early stages of the infection. However, it's important to recognize that not all patients will exhibit this hallmark sign.

In fact, studies indicate that erythema migrans occurs in approximately 70-80% of those diagnosed with Lyme disease, meaning that it does not occur in about 20-30% of cases. This statistic aligns with the answer selected. Many patients may experience Lyme disease without presenting any rash, especially if they were infected later in the season or if the tick attachment was not recognized, which can contribute to the absence of the erythema migrans rash.

Understanding the prevalence of erythema migrans is crucial for healthcare professionals. It emphasizes the need for a comprehensive evaluation of symptoms and potential exposure to ticks in diagnosing Lyme disease, especially in patients who do not display this characteristic rash.