Classification of the episode
The correct classification is
pseudo-relapse, which requires no modification of the disease-modifying therapy or acute corticosteroid treatment.
A
pseudo-relapse is a transient reappearance or worsening of
pre-existing neurological symptoms triggered by a systemic stressor such as fever, infection, dehydration, or heat exposure. In this case, the patient experienced burning on urination and a temperature of
38.5 °C, both consistent with a urinary tract infection. Her old symptoms of leg numbness and weakness worsened during the febrile period and then returned to baseline within
2 days after the infection was treated. No new neurological deficit appeared.
A true MS relapse is defined by new or worsening neurological symptoms lasting more than 24 hours in the absence of fever or infection. Because this patient’s symptoms were old, occurred in the setting of fever and infection, and resolved once the trigger was eliminated, the episode does not meet the criteria for a true relapse. Consequently, high-dose corticosteroids are not indicated, and there is no evidence of disease progression to a secondary progressive course.
Key point! Fever itself can impair conduction through previously demyelinated axons. Elevated body temperature slows or blocks saltatory conduction in areas where the myelin sheath is already damaged, causing old symptoms to resurface temporarily. This is a physiological phenomenon, not new inflammatory disease activity.
Watch out! Urinary tract infections are among the most common triggers of pseudo-relapse in persons with MS. The evaluation of any suspected relapse should therefore include a search for infection, fever, or metabolic derangement before concluding that new inflammatory activity has occurred
[2].
The distinction between relapse and pseudo-relapse carries direct treatment implications. A true relapse that is functionally bothersome may warrant timely corticosteroid therapy to accelerate recovery and limit disability
[2]. A pseudo-relapse, by contrast, is managed by treating the underlying trigger. Changing the disease-modifying regimen or administering steroids in this scenario would expose the patient to unnecessary risk without addressing the actual cause of the transient worsening.
| Feature | Pseudo-relapse | True relapse |
|---|
| Symptoms | Old symptoms reappear or worsen | New symptoms or clear worsening of old ones |
| Trigger | Fever, infection, heat, stress | No identifiable systemic trigger |
| Duration | Variable; resolves when trigger is treated | Persists beyond 24 hours |
| Pathophysiology | Conduction block in previously demyelinated axons | New inflammatory demyelination |
| Treatment | Treat the underlying trigger | Consider corticosteroids if functionally significant |
Infections are recognized as being associated with an increased risk of both relapse and pseudo-relapse in individuals with MS . The clinical challenge is to determine which process is occurring in a given patient. When fever and infection are present, the safest initial interpretation is that the neurological worsening represents a pseudo-relapse until proven otherwise. The patient’s rapid return to her usual baseline after treatment of the urinary tract infection confirms this interpretation.
References (research sources)