Differential Diagnosis for Lyme Disease Test Results

The provided test results indicate a negative Lyme IgG and IgM Line Blot interpretation, with the exception of a present IgM P23 Ab. Given these results, the following differential diagnoses are considered:

• Single Most Likely Diagnosis
  • Early Lyme Disease: The presence of IgM P23 Ab suggests early infection, as IgM antibodies are typically elevated in the initial stages of Lyme disease. However, the negative IgG and IgM Line Blot interpretations and the absence of other specific antibodies (e.g., P41, P39) may indicate a very early stage of the disease or a false-positive result.
• Other Likely Diagnoses
  • False-Positive Result: The isolated presence of IgM P23 Ab without other supporting antibodies or clinical symptoms may indicate a false-positive result.
  • Other Tick-Borne Illnesses: The patient may be infected with another tick-borne disease, such as anaplasmosis, babesiosis, or ehrlichiosis, which can present with similar symptoms to Lyme disease.
• Do Not Miss Diagnoses
  • Neuroborreliosis: Although the test results are largely negative, it is essential to consider neuroborreliosis, a serious complication of Lyme disease that can occur even with negative serology. Clinical symptoms such as meningitis, encephalitis, or radiculopathy would warrant further investigation.
  • Lyme Carditis: Another potentially life-threatening complication of Lyme disease, Lyme carditis can occur even with negative serology. Symptoms such as heart block or arrhythmias would necessitate prompt evaluation.
• Rare Diagnoses
  • Southern Tick-Associated Rash Illness (STARI): A rare condition characterized by a rash similar to erythema migrans, STARI is associated with the lone star tick and may not be detected by standard Lyme disease tests.
  • Tick-Borne Relapsing Fever: A rare disease caused by Borrelia species, tick-borne relapsing fever can present with recurring episodes of fever, headache, and muscle pain, and may not be detected by standard Lyme disease tests.

It is essential to note that the diagnosis of Lyme disease should be based on a combination of clinical symptoms, epidemiological history, and laboratory results, using a two-tiered approach as recommended by current guidelines. The provided test results should be interpreted in the context of the patient's overall clinical presentation and medical history.