QuestionSBA
QuestionChoice
Streptococcal infections are associated with erythema nodosum, but there is nothing in the history to suggest that this may be the cause in this case
32311
d
Post-streptococcal infection
QuestionChoice
The lesions described are typical of erythema nodosum. This is an inflammatory disorder affecting the subcutaneous fat. The cause is unknown in approximately 55% of patients, and most cases resolve within days to weeks
32308
a
Idiopathic
QuestionChoice
Sarcoidosis is an important cause of erythema nodosum; however, the normal chest x-ray, blood tests and absence of symptoms make this unlikely
32310
c
Sarcoidosis
QuestionChoice
IBD is associated with erythema nodosum. The normal blood tests and absence of gastrointestinal or systemic symptoms would make this unlikely in this case
32312
e
Inflammatory bowel disease (IBD)
QuestionChoice
TB is an important cause of erythema nodosum; however, the absence of systemic symptoms, risk factors and normal chest x-ray makes this unlikely
32309
b
Tuberculosis (TB)
Concept
Chapter
# Summary

Erythema nodosum is a panniculitis subtype characterised by tender, red, raised nodules typically affecting the shins. The cause is often idiopathic, although associations with certain medications and diseases like sarcoidosis and inflammatory bowel disease are known. Diagnosis is clinical, with the disease usually resolving spontaneously. Management primarily focuses on treating the underlying cause, if identified, and providing symptomatic relief.

# Definition

Erythema nodosum represents a form of panniculitis, or inflammation of the subcutaneous fat, which manifests as tender, raised, erythematous nodules predominantly affecting the shin area.

# Epidemiology

Erythema nodosum affects a broad range of individuals and is more common in women than men. Although it can occur at any age, it typically affects individuals between 20-30 years of age.

# Aetiology

The aetiology of erythema nodosum is often idiopathic, accounting for up to 50% of cases. Other identifiable causes, conveniently remembered by the acronym **NODOSUM**, include:

- **NO** cause (Idiopathic)
- **D**rugs, particularly sulfonamides and dapsone
- **O**ral contraceptive pill (OCP)
- **S**arcoidosis
- **U**lcerative colitis and Crohn's disease
- **M**icroorganisms: Tuberculosis, Streptococcus, Toxoplasmosis

# Signs and Symptoms

Clinically, erythema nodosum presents as:

- Tender, raised, red or violet nodules, usually located on the anterior surface of the legs.
- Accompanied by systemic symptoms such as fever, malaise, and arthralgia in some cases.

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# Differential Diagnosis

The differential diagnoses for erythema nodosum and their key signs and symptoms include:

- **Cellulitis**: Characterised by local warmth, redness, swelling and tenderness, fever, and possibly lymphadenopathy.
- **Deep vein thrombosis (DVT)**: Presents with pain, swelling, and redness of the affected limb; Homan's sign might be present.
- **Necrobiosis lipoidica**: Typically presents as shiny, reddish-brown patches which slowly grow into larger plaques with a yellowish centre.
- **Vasculitis**: Manifests with palpable purpura, ulcers, or digital infarcts.

# Investigations

While erythema nodosum is primarily diagnosed clinically, additional investigations may be performed to rule out underlying causes. These can include:

- Full Blood Count (FBC)
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP)
- Throat culture for streptococci
- Chest x-ray (to rule out sarcoidosis or tuberculosis)
- Tests for inflammatory bowel disease if suspected (e.g. colonoscopy)


# Management

The management of erythema nodosum primarily involves treating the underlying cause, if identified. Additional strategies include:

- Nonsteroidal anti-inflammatory drugs (NSAIDs) to alleviate pain and inflammation
- Rest and leg elevation
- Potassium iodide or colchicine may be used in severe cases
- Corticosteroids are used sparingly and typically reserved for severe, refractory cases

# References

[Erythema Nodosum - DermNet NZ](https://dermnetnz.org/topics/erythema-nodosum)
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An example of erythema nodosum on the shins.
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Another example of erythema nodosum on the shins.
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Erythema Nodosum
Topic
4
Dermatology
6462
Erythema nodosum presents as tender red nodules on the shins and often has an idiopathic aetiology, resolving spontaneously within weeks.
A 24-year-old patient presents with tender red nodules on the anterior shins that developed over the last week. Full systems review is negative, and the patient cannot find any triggers that may have lead to the lesions.

A chest x-ray and initial blood tests are normal.

Which of the following is the most likely cause of this patient's rash?
a