Differential Diagnosis
- Single most likely diagnosis
- Lyme disease: This is the most likely diagnosis given the patient's symptoms of headaches, diffuse joint pain, and fatigue, combined with a skin lesion (likely erythema migrans) after hiking in Connecticut, an area known to have a high incidence of Lyme disease.
- Other Likely diagnoses
- Southern tick-associated rash illness (STARI): Although less common than Lyme disease, STARI can present with a similar rash and symptoms after a tick bite, primarily in the southern United States, but it's less likely given the location of Connecticut.
- Anaplasmosis: This tick-borne illness can cause symptoms similar to Lyme disease, including fever, headache, and joint pain, but it typically does not present with a distinctive skin lesion.
- Babesiosis: Another tick-borne disease that can cause fever, fatigue, and joint pain, but it often presents with hemolytic anemia, which is not mentioned in the scenario.
- Do Not Miss (ddxs that may not be likely, but would be deadly if missed.)
- Rocky Mountain spotted fever (RMSF): Although less common in Connecticut, RMSF is a potentially life-threatening tick-borne illness that requires prompt diagnosis and treatment. It presents with fever, headache, and a rash, but the rash can appear later in the course of the disease.
- Ehrlichiosis: Similar to anaplasmosis, ehrlichiosis is a tick-borne disease that can cause severe illness, including fever, headache, and fatigue, and can be life-threatening if not treated promptly.
- Rare diagnoses
- Tularemia: A rare tick-borne or insect-borne disease that can cause fever, headache, and rash, but it is less common and typically associated with specific exposures (e.g., handling infected rabbits).
- Tick-borne relapsing fever: Caused by different species of Borrelia, this disease is rare in the northeastern United States and typically presents with recurrent episodes of fever, headache, and joint pain.
Next Step in Management
Given the clinical presentation and the presence of a skin lesion consistent with erythema migrans, the most appropriate next step would be to confirm the diagnosis of Lyme disease. Among the options provided:
- B. Enzyme-Linked Immunosorbent Assay (ELISA) Assay is typically the first step in diagnosing Lyme disease, followed by a Western blot test for confirmation if the ELISA is positive or equivocal. However, in early disease with a clear erythema migrans lesion, treatment may be initiated empirically without waiting for serologic confirmation.
- Therefore, D. No need for testing; begin empiric treatment with doxycycline could be considered the most appropriate next step, especially if the clinical presentation is highly suggestive of Lyme disease, as it seems to be in this case. Empiric treatment is often recommended for patients with erythema migrans to prevent the progression of the disease.