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Erythema Multiforme vs Erythema Migrans [High-yield Notes]

August 16, 2023

In the realm of dermatology, where skin conditions often present themselves as very complex puzzles, two distinct entities stand out: Erythema Multiforme and Erythema Migrans. While they share a similar abbreviation, these two conditions couldn’t be more different in terms of their underlying causes, pathophysiology, clinical presentations, and implications for patient care.

As we dive into this educational journey, allow me, a seasoned medical professional, to walk you through the key points that differentiate these two skin conditions. Beyond their mere names lies a tremendous wealth of knowledge that holds significance for healthcare professionals and individuals seeking a deeper understanding of these skin manifestations.

Erythema Multiforme, characterized by its enigmatic “target lesions”, often leaves patients and clinicians alike intrigued by its diverse triggers and potential complications if not treated soon. On the other hand, Erythema Migrans, synonymous with Lyme disease, is a dermatological sentinel, presents with a “bull’s-eye” appearing rash — a warning sign of a much larger systemic concern.

In this comprehensive blog post, we will dissect the clinical features, etiology, diagnostic approaches, treatment strategies, and potential complications associated with both Erythema Multiforme and Erythema Migrans. We hope that you find this blog post useful! 🙂

Erythema Multiforme vs Erythema Migrans

Below are the important differences between erythema multiforme and erythema migrans. All these points are high-yield for medical students and doctors. 🙂

Characteristics	Erythema Multiforme	Erythema Migrans
Slide	“A maculopapular rash appearing usually on palms and feet, often pruritic and blanches away slowly”	“Bull’s-eye” appearance; central erythema and necrosis; expands rather than migrating.
Definition	Erythema Multiforme is an acute, immune-mediated skin disorder characterized by target-like lesions. It can be triggered by infections, drugs, or other factors (important causes have been discussed below).	Erythema Migrans is the characteristic skin rash associated with Lyme disease, caused by the spirochete bacterium Borrelia burgdorferi. It’s a red rash with a central clearing that looks like a “bull’s eye.”
Cause	Infections: Herpes simplex virus (most common cause) * Mycoplasma pneumonia Cytomegalovirus (CMV) Epstein-Barr virus (EBV) Other viral infections Medications: Certain antibiotics (e.g., penicillins, sulfa drugs) Antiepileptic medications (e.g., phenytoin) Nonsteroidal anti-inflammatory drugs (NSAIDs) Allopurinol (used for gout) Other Factors: Idiopathic (unknown cause) Autoimmune disorders (rarely) Malignancies (rarely)	Bacterial Infection: Borrelia burgdorferi infection (primary cause) Transmitted through the bite of infected ticks, typically Ixodes scapularis (black-legged ticks) most commonly found in North America and Ixodes ricinus in Europe.
Lesion Appearance	Target-like or iris lesions, with concentric rings of various colors (red, pale, and normal skin tone).	Circular or oval-shaped rash with central clearing, resembling a bull’s-eye.
Distribution of lesion	Can affect any part of the body, mainly the extremities, face, trunk, palms, and soles.	Typically occurs at the site of the tick bite and expands gradually over the period of time.
Systemic Symptoms	Can be associated with mild constitutional symptoms or mucous membrane involvement.	May be accompanied by flu-like symptoms such as fever, lethargy, fatigue, headache, and muscle aches.
Duration	Acute and self-limiting, with lesions resolving within weeks.	The rash can last for several weeks if left untreated.
Treatment	Depends on the underlying cause. Supportive care for mild cases; discontinuation of triggering medications.	Treatment usually involves antibiotics like Doxycycline or Amoxicillin for Lyme disease.
Complications	Can recur or progress to a more severe form called Stevens-Johnson syndrome or toxic epidermal necrolysis (TEN).	If left untreated, Lyme disease can lead to more serious systemic complications affecting the joints, heart, and nervous system.
Geographic Occurrence	Worldwide distribution.	Common in areas with high tick populations, particularly in warm regions of North America, Europe, and Asia.
Prevention	Avoidance of triggers (like certain infections or medications).	Prevent tick bites by wearing protective clothing, using insect repellents, and checking for ticks on clothing and body after outdoor activities.
Diagnostic Markers	Diagnosis is primarily clinical based on lesion appearance and patient history.	Diagnosis is based on clinical signs, symptoms, and history of potential exposure to ticks in an endemic area. Laboratory tests like serology can confirm Lyme disease.