Derm Dx: Rash on the Leg Following Outdoor Activity

Slide

Case Study:
Explanation:

A 42-year-old man requests a dermatologic evaluation by emailing an image of a rash on his leg that he is concerned about. The patient developed the rash approximately 2 weeks ago and was diagnosed with cellulitis at a local urgent care center. Despite 10 days of cephalosporin therapy, the rash has persisted, and new “blotches” have appeared on his back and arms. He reports that the rash is asymptomatic, and he has remained afebrile throughout the course. The patient’s medical history is positive for psoriasis and psoriatic arthritis. He states that he has recently spent a significant amount of time outdoors but denies receiving a recent tick bite.

Can you diagnose this condition?

Lyme disease is a tickborne illness caused by Borrelia burgdorferi, bacteria known as spirochetes because of their corkscrew shape. The tick Ixodes scapularis is the primary vector that transmits the bacteria in the United States. Cases are reported primarily in...

Submit your diagnosis to see full explanation.

Lyme disease is a tickborne illness caused by Borrelia burgdorferi, bacteria known as spirochetes because of their corkscrew shape. The tick Ixodes scapularis is the primary vector that transmits the bacteria in the United States. Cases are reported primarily in the Midwest and the Northeast and most frequently occur between the months of May and September.¹ Medical history typically includes recent outdoor activity in a wooded area with development of flu-like symptoms and a rash following a tick bite. For disease transmission to be possible, the tick must remain attached for at least 24 hours. The incubation period ranges from 3 to 20 days.^2,3 The pathognomonic dermatologic finding in Lyme disease is erythema migrans, a characteristic patch with central clearing. It occurs at the site of the tick bite and is found in a majority of cases.

Diagnosis of early Lyme disease can be made by recognizing the classic rash with or without a history of a tick bite in endemic areas. Confirmation is established by serologic testing. First-line treatment for early disease is doxycycline.^1,4

Sarah Jacobs, PA-S, is a physician assistant student at Kings College, in Wilkes Barre, Pennsylvania; and Stephen Schleicher, MD, is director of the DermDox Center for Dermatology, as well as an associate professor of medicine at Commonwealth Medical College and a clinical instructor of dermatology at Arcadia University and Kings College.

References

1. Treatment of Lyme disease. Med Lett Drugs Ther. 2016;58(1494):57-58.

2. Eisen L. Pathogen transmission in relation to duration of attachment by Ixodes scapularis ticks. Ticks Tick Borne Dis. 2018;9(3):535-542.

3. Richardson M, Elliman D, Maguire H, Simpson J, Nicoll A. Evidence base of incubation periods, periods of infectiousness and exclusion policies for the control of communicable diseases in schools and preschools. Pediatr Infect Dis J. 2001;20(4):380-391.

4. Sanchez E, Vannier E, Wormser GP, Hu LT. Diagnosis, treatment, and prevention of Lyme disease, human granulocytic anaplasmosis, and babesiosis: a review. JAMA. 2016;315(16):1767-1777.