What is the possible diagnosis for a patient with a low-grade fever, unilateral cervical adenitis, and tiredness, who developed numbness and tingling sensations after taking doxycycline (a tetracycline antibiotic)?

Possible Diagnosis: Lyme Disease with Neurologic Involvement (Neuroborreliosis)

The most likely diagnosis is Lyme disease with early neurologic involvement (neuroborreliosis), presenting as cranial neuropathy and peripheral neuropathy following initial treatment with doxycycline for what appeared to be early localized infection.

Clinical Reasoning

The patient's presentation follows a classic pattern for Lyme disease progression:

Initial Presentation Consistent with Early Lyme Disease

• Low-grade fever for 4 days with unilateral cervical adenitis suggests early localized infection 1
• Mild leukopenia (WBC 3200) and normal platelets (210,000) are consistent with early Lyme disease rather than rickettsial illness 2
• The dramatic response to a single dose of doxycycline (fever resolution) is characteristic of early Lyme disease 1

Development of Neurologic Complications

• The appearance of unilateral facial numbness/tingling with ipsilateral hand paresthesias 2 days after starting doxycycline strongly suggests early disseminated Lyme disease with neurologic involvement 2, 1
• The severe pain triggered by air movement (allodynia) indicates neuropathic pain, consistent with cranial or peripheral neuropathy 2
• Absence of motor deficits is typical for early neuroborreliosis, which primarily affects sensory nerves initially 2

Critical Diagnostic Pitfall

The patient likely received inadequate treatment duration for Lyme disease. A single capsule of doxycycline is insufficient—even early localized Lyme disease requires 10-28 days of treatment 2, 1. The brief exposure may have:

• Temporarily suppressed symptoms (explaining fever resolution)
• Failed to prevent dissemination to the nervous system
• Allowed progression to early disseminated disease with neurologic manifestations 2

Why This Is NOT a Tickborne Rickettsial Disease

Several features argue against rickettsial illness (RMSF, ehrlichiosis, anaplasmosis):

• Normal platelet count (210,000): Thrombocytopenia is nearly universal in rickettsial diseases, with platelets typically <100,000 2
• Mild leukopenia without severe systemic illness: Rickettsial diseases typically present with more profound leukopenia and clinical deterioration 2
• Unilateral cervical adenitis: This is characteristic of Lyme disease but not typical of rickettsial infections 1
• Development of isolated neuropathy without multisystem involvement: Rickettsial diseases cause vasculitis affecting multiple organs simultaneously 2

Recommended Management

Immediate Actions

• Switch to appropriate treatment for neuroborreliosis: doxycycline 100 mg twice daily for 28 days 2
• Alternative: amoxicillin 500 mg three times daily for 28 days if doxycycline is contraindicated 2
• For severe neurologic involvement or treatment failure, consider intravenous ceftriaxone 2 g daily for 14-28 days 2

Diagnostic Confirmation

• Obtain Lyme serology (IgM and IgG antibodies to Borrelia burgdorferi) 1
• Consider lumbar puncture if symptoms worsen or new neurologic signs develop, looking for lymphocytic pleocytosis and elevated protein 2
• Document tick exposure history and geographic risk factors (Northeast, upper Midwest, or northern California) 1

Monitoring

• Close follow-up within 48-72 hours to assess response to appropriate antibiotic therapy 2
• Neurologic symptoms should begin improving within 1-2 weeks of adequate treatment 2
• Persistent or worsening symptoms despite oral therapy warrant consideration of intravenous antibiotics 2

Important Caveat

Five patients in a major Lyme arthritis treatment study developed neuroborreliosis during oral antibiotic therapy, all of whom had subtle neurologic symptoms at baseline 2. This underscores the importance of:

• Careful neurologic examination before initiating treatment
• Extended treatment duration (28 days minimum) for any suspected neurologic involvement
• Low threshold for switching to intravenous therapy if symptoms progress 2