What is considered a high fever in patients with multiple sclerosis?

Fever Thresholds in Multiple Sclerosis Patients

In patients with multiple sclerosis, a temperature of ≥38°C (100.4°F) is considered a high fever and should be treated aggressively due to the risk of temporary worsening of neurological symptoms (Uhthoff's phenomenon). 1, 2

Definition of Fever in Multiple Sclerosis

• A single oral temperature of ≥38°C (100.4°F) is considered fever with high specificity (90%) for infection in the general population, including MS patients 3
• In MS patients specifically, any temperature elevation is concerning as 60-80% experience temporary worsening of clinical signs and neurologic symptoms with even mild heat exposure 1, 2
• Repeated oral temperatures ≥99°F (37.2°C) should be monitored closely in MS patients as even this level may trigger symptom exacerbation 3, 2

Clinical Significance in Multiple Sclerosis

• Temperature elevations in MS patients can cause:

  • Conduction slowing in demyelinated axons 1
  • Conduction block in neural pathways 1, 2
  • Temporary worsening of existing symptoms 2
  • Appearance of new neurological symptoms not previously experienced 4

• MS patients show increased clinic visits during periods of higher ambient temperatures and temperature variations 5

• Spring, summer, and fall months show 9% higher MS clinic visits compared to winter months 5

Special Considerations for MS Patients

• MS lesions can occur in brain areas responsible for thermoregulation, potentially impairing temperature control 1
• MS patients may have reduced sweating responses due to impaired neural control of sudomotor pathways 1
• Both increases AND decreases in body temperature can trigger symptom exacerbation in MS patients 2
• Temperature variations (standard deviation of temperature) show the strongest association with MS symptom exacerbation 5

Management Approach

• Fever in MS patients should be treated promptly with antipyretics to prevent symptom worsening 6
• Sources of fever should be identified and treated appropriately 6
• Pre-cooling therapy can be used to prevent symptom worsening during anticipated heat exposure 7
• Active cooling methods (circulating liquid garments) and passive cooling methods (ice or gel packs) have shown benefit in preventing heat-related symptom exacerbation 7

Common Pitfalls to Avoid

• Failing to recognize that even mild temperature elevations (below traditional fever thresholds) can worsen MS symptoms 1, 2
• Not considering non-temperature signs of infection in MS patients, as fever response may be altered 8
• Overlooking that temperature variations, not just absolute temperature, can trigger MS exacerbations 5
• Ignoring the impact of ambient temperature and humidity on MS symptom presentation 5

Monitoring Recommendations

• Regular temperature monitoring during infections or heat exposure 3, 1
• Consistent temperature measurement method (preferably oral or rectal) 9
• Monitoring for new or worsening neurological symptoms with any temperature elevation 1, 4
• Particular vigilance during seasonal temperature changes and variations 5