How to manage a 77-year-old male with Lyme disease on doxycycline, presenting with joint swelling and hyponatremia and hypochloremia?

Management of Hyponatremia and Hypochloremia in a 77-Year-Old Male with Lyme Disease on Doxycycline

The 77-year-old male with Lyme disease on doxycycline who presents with joint swelling and electrolyte abnormalities should be evaluated for syndrome of inappropriate antidiuretic hormone secretion (SIADH) or other causes of hyponatremia, and doxycycline should be continued for the full recommended course of 14-21 days for Lyme disease. 1

Assessment of Electrolyte Abnormalities

The patient presents with:

• Hyponatremia (130 mmol/L, reference range 135-146 mmol/L)
• Hypochloremia (94 mmol/L, reference range 98-110 mmol/L)
• Normal kidney function (eGFR 95 mL/min/1.73m²)
• Joint swelling while on doxycycline for Lyme disease

Differential Diagnosis for Hyponatremia

1. Medication-related:

   • Doxycycline itself is not typically associated with hyponatremia, but careful review of all medications is warranted

2. SIADH - Consider this diagnosis given:

   • Age (77 years)
   • Normal kidney function
   • No evidence of volume depletion based on labs

3. Other causes to consider:

   • Excessive fluid intake
   • Heart failure
   • Liver disease
   • Adrenal insufficiency
   • Hypothyroidism

Management Approach

1. Continue Appropriate Lyme Disease Treatment

• Maintain doxycycline therapy at 100mg twice daily 1
  • The American College of Rheumatology recommends doxycycline as first-line therapy for adults with Lyme disease
  • Complete the full course (14-21 days for early Lyme disease)
  • Monitor for doxycycline side effects including photosensitivity and GI symptoms 2

2. Evaluate and Manage Hyponatremia

• Assess volume status clinically

• Order additional tests:

  • Serum osmolality
  • Urine sodium and osmolality
  • TSH and morning cortisol
  • Consider chest imaging to rule out occult malignancy (a cause of SIADH)

• Management based on severity and symptoms:

  • If asymptomatic (likely in this case given mild hyponatremia):
    • Fluid restriction (800-1000 mL/day)
    • Monitor electrolytes every 1-2 days until stable
  • If symptomatic or sodium <125 mmol/L:
    • Consider hospitalization for closer monitoring
    • More aggressive intervention may be needed

3. Address Joint Swelling

• Evaluate if joint swelling represents:

  • Lyme arthritis (requiring continued antibiotic therapy)
  • Inflammatory response to treatment (Jarisch-Herxheimer reaction)
  • Alternative diagnosis

• Management approach:

  • NSAIDs for symptomatic relief if not contraindicated
  • Joint aspiration if effusion is significant to rule out septic arthritis
  • Consider rheumatology consultation if symptoms persist beyond antibiotic course

Monitoring and Follow-up

• Electrolytes: Monitor sodium and chloride levels every 1-2 days until stable, then weekly
• Clinical reassessment: At 7-10 days to ensure symptom improvement 1
• Complete antibiotic course: 14-21 days total for early Lyme disease 1

Important Considerations and Pitfalls

• Avoid rapid correction of hyponatremia as it can lead to osmotic demyelination syndrome

• Do not discontinue doxycycline prematurely despite electrolyte abnormalities unless clear evidence links the medication to these changes

• Beware of fluid overload in elderly patients when correcting electrolyte abnormalities

• Consider drug interactions with doxycycline, particularly:

  • Antacids containing aluminum, calcium, or magnesium
  • Iron-containing preparations
  • Anticoagulants (may require dose adjustment) 2

• Avoid extended antibiotic courses beyond recommended durations for Lyme disease, as this increases risk of adverse effects without proven benefit 1