Erythema Nodosum

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Erythema nodosum (EN)\: a painful, in
nodules and plaques, typically on the anterior shins.
Demographics\: Six times more common in women, typically a
persons.
Aetiology\: Hypersensitivity reaction of unknown cause, triggered by infections (e.g., streptococcal, tuberculosis,
mycoplasma), in
(e.g., lymphoma, leukemia), and pregnancy. Approximately 50% are idiopathic.
Histopathology\: EN is a septal panniculitis without vasculitis. Di
(connective tissue) or lobular (fat lobules).
Prodrome\: May include arthralgia (ankles and knees), malaise, and fever 1-3 weeks before rash onset.
Rash\: Tender, warm, erythematous subcutaneous nodules and plaques, often on anterior lower legs. Lesions are
initially, later becoming
Symmetrical and bilateral distribution.
Di
lipodermatosclerosis).
Investigations\: Primarily clinical diagnosis. Bedside\: urine pregnancy test. Laboratory\: FBC, CRP, ESR (raised in EN), throat
swab (streptococcus), ASOT, tuberculin skin test, IGRA. Imaging\: chest X-ray for hilar lymphadenopathy. Additional\: serum
ACE and calcium (sarcoidosis), viral serology, stool culture, colonoscopy, excisional skin biopsy if diagnosis is uncertain.
Management\: Typically self-limiting, focus on treating underlying condition and supportive care. Supportive measures\: bed
rest, limb elevation and compression, NSAIDs for pain, discontinue causative drugs, treat underlying cause. Short-term oral
potassium iodide may be used in problematic cases but avoid prolonged use due to hyperthyroidism risk.
Complications\: EN usually resolves within six weeks without scarring. Arthralgia may persist up to two years.
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Introduction

Erythema nodosum (EN) is a painful, in
(panniculitis). It commonly presents as tender, erythematous nodules and plaques on the anterior shins.
EN is six times more common in women and typically a
Erythema nodosum occurs in approximately one to
1,2

Aetiology

Erythema nodosum is thought to be a hypersensitivity reaction of unknown cause. It can be triggered by several di
stimuli or systemic conditions (Table 1).
2
Approximately 50% of cases are classi
4Table 1. Possible triggers of erythema nodosum (most common triggers highlighted in bold).
1,2,3,5
Category Triggers
Idiopathic
Infections
Streptococcal infections,
especially pharyngitis (most
common infectious cause)
Tuberculosis infection
Mycoplasma infection
Salmonella infection
Yersiniosis infection
Chlamydia trachomatis infection
Viral infections (rare) including
herpes simplex virus, Epstein Barr
virus,
human immunode
(HIV)
and viral hepatitis
In
(Crohn's disease/
ulcerative colitis
In
)
Sarcoidosis
Behcet's disease
Drugs
Antibiotics (e.g. sulphonamides,
penicillin)
Oral contraceptive/oestrogens
Malignancies
Lymphoma
Leukaemia
Other Pregnancy
Histopathology
Panniculitis is di
predominantly septal (in
vasculitis.
Erythema nodosum is the most common form of panniculitis and is classi
3
Other types of septal panniculitis include necrobiosis lipoidica and lipodermatosclerosis. Nodular vasculitis is an example
of a lobular panniculitis with vasculitis.
3

Clinical features

Prodrome
A prodrome of arthralgia, commonly of the ankles and knees, malaise and fever may occur one to three weeks before the
onset of the classical rash.
4,6,7
Rash
Erythema nodosum classically presents as tender, warm, erythematous subcutaneous nodules and plaques. These
lesions are often poorly de
3,7The distribution of lesions typically involves the anterior aspect of the lower legs, however, lesions can occur anywhere.
The nodules and plaques tend to be symmetrical and bilateral.
Initially, the subcutaneous nodules are
The lesions tend to be bright to deep red and then typically fade to dusky blue/purple then yellow, resembling a resolving
bruise. 3 1,7
However, lesions are sometimes better palpated than visualised.
Ankle swelling, alongside arthralgia, is often associated with erythema nodosum.
3
Figure 1. Erythema nodosum on the lower limbs in a person who recently had streptococcal pharyngitis.
8
Figure 2. Erythema nodosum on the lower limbs in a person with darker skin tone.
9Figure 3. Typical red nodule of erythema nodosum.
10

Di

Di
Trauma
Cellulitis and erysipelas
Other types of panniculitis including nodular vasculitis and lipodermatosclerosis

Investigations

Erythema nodosum is usually a clinical diagnosis.
3
It is important to investigate potential underlying causes and conditions. Due to the vast number of underlying causes, a
thorough and detailed history and examination must be performed to guide the investigation strategy.
Bedside investigations
Relevant bedside investigations include\:
Urine pregnancy test (human chorionic gonadotropin (hCG) urine dipstick)
Laboratory investigations
Relevant laboratory investigations include\:
Baseline blood tests (FBC, CRP, ESR)\: in
Throat swab for microscopy, culture & sensitivity and anti-streptolysin-O titre (ASOT)\: swab is positive for streptococcus
in current streptococcal infection and ASOT is elevated in recent streptococcal infection
Tuberculin skin test or interferon-gamma release assay (IGRA)\: positive in tuberculosis
ImagingRelevant imaging investigations include\:Chest X-ray\: hilar lymphadenopathy may indicate sarcoidosis, tuberculosis, mycoplasma or lymphoma
Additional investigations
Additional investigations to consider may include\:
Serum ACE and calcium\: elevated in sarcoidosis
Viral titres and serology\: to assess for herpes simplex virus, Epstein-Barr virus, hepatitis B and C virus and HIV
Stool culture, including ova and parasites (if diarrhoeal symptoms present)\: to assess for gastrointestinal infection
Colonoscopy (if gastrointestinal symptoms present)\: to assess for in
Excisional skin biopsy\: if the clinical diagnosis is in doubt, a biopsy is particularly useful in di
predominantly septal or lobular panniculitis.
1,3,7

Management

Erythema nodosum is usually self-limiting and treatment should be aimed at managing the underlying condition and
providing supportive therapies.
5,7
Supportive management may include\:
1
Bed rest
Elevation and compression of a
Non-steroidal anti-in
Stop any causative drugs
Treatment of any underlying cause
Short-term oral potassium iodide may be useful in particularly problematic cases, however, prolonged use should be
avoided due to the risk of hyperthyroidism

Complications

Erythema nodosum usually resolves within six weeks, without scarring. 6
period can continue for up to two years.
2,7
However, arthralgia related to the prodrome

References

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DermNet NZ. E r y t h e m a n o d o s u m . Published in 2019. Available from\: [LINK].
J. Cowan and M. Graham. E v a l u a t i n g t h e c l i n i c a l s i g n i
[LINK].
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M. Chowaniec, A. Starba and P. Wiland. E r y t h e m a n o d o s u m - r e v i e w o f t h e l i t e r a t u r e . Published in 2016. Available from\:
[LINK].
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J. Heilman. E r y t h e m a n o d o s u m o n t h e l o w e r l i m b s i n a p e r s o n w h o h a d r e c e n t l y h a d s t r e p t o c o c c a l p h a r y n gi t i s . BY-SA]. Available from\: [LINK].
Licence [CC
Medicalpal. E r y t h e m a n o d o s u m o n t h e l o w e r l i m b s i n a p e r s o n w i t h d a r k e r s k i n t o n e . Licence [CC BY-SA]. Available from\:
[LINK].
Ganguly. T y p i c a l r e d n o d u l e o f e r y t h e m a n o d o s u m . Licence [CC BY]. Available from\: [LINK].Reviewer
Dr Tom King
Dermatology Consultant

Related notes

Acne vulgaris
Basal Cell Carcinoma (BCC)
Cellulitis
Cutaneous Squamous Cell Carcinoma (SCC)
Erythema Multiforme

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Contents

Introduction
Aetiology
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