Dermatology Clinic

A 25 year old male presents to the Emergency Department complaining of a rash to his left side. The patient stated he first noticed it after waking up 3 hours before coming to the ER. The patient denied any associated symptoms including pain, pruritus, fever, chills, myalgias, arthralgias, fatigue, headache, weakness, or swelling of lymph nodes. He further denied any new soaps, detergents, foods, medications, or topical products. ROS was otherwise negative, the patient denied no prior medical problems. The patient did report working outdoors as a landscaper but denied any known insect bites, recent wounds to affected area, or past contact allergies to plants.

Clinically, the patient was a well developed, well nourished, 25 year old male in no distress or discomfort, and appeared in excellent health. Vital signs showed he was afebrile and normotensive with a normal pulse rate. His exam was unremarkable save for the rash that appeared as follows:


I’m sure most will recognize the large bull’s eye pattern to the rash, which combined with the patient’s history of working outdoors created the concern for Lyme Disease. The patient was started on the appropriate course of Doxycycline, Lyme Titers were sent which ultimately returned positive as well as follow up testing.

While Lyme Disease is not uncommon and it’s associated bull’s eye rash is usually easily identified, I felt this case was worthy of note to make some finer points about the disease.

1) Lack of Symptoms: While we all learn about the constitutional symptoms (arthralgia, fevers, etc.) of Lyme Disease, it is not necessary to have them all as demonstrated by this case.

2) Time of Onset of Rash: While the average time of onset of a bull’s eye rash is 7 days, it can occur anywhere from 3 to 30 days after a tick bite. Combined with the fact that Lyme Tests typically will not seroconvert to positive for about 3 weeks and this patient tested positive from the first test, this patient did not develop the bull’s eye rash until roughly day 21 post exposure.

3) Size/Location of Rash: It can be easy to assume that the bull’s eye rash will be smaller in size. Indeed a simple google image search show most (not all) of the bull’s eye rashes to be smaller in size. In addition, they are seen on expected locations such as extremities and trunk, as with the case above. However, since the rash first appears at the site of the tick bite, the rash can occur anywhere including less thought about places such as the groin or scalp, the latter of which can be obstructed by hair.


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