On this page & tools
Write your answer
Saved on this device. No marking — you are the marker.
Q1: Definition and clinical presentation (2 min)
Examiner: A 28-year-old woman has bilateral tender red nodules on her shins. What is the most likely diagnosis and what is its essential pathology?[1]
Candidate: Erythema nodosum — an acute septal panniculitis, the commonest panniculitis. Bilateral, symmetric, tender, erythematous subcutaneous nodules on the anterior shins. It never ulcerates and never scars; the nodules resolve like a bruise over two to six weeks. Histologically it is inflammation of the connective-tissue septa with sparing of the fat lobules and — critically — no vasculitis.[1][3]
Examiner (push): Why does it not ulcerate?[3]
Candidate: Because the blood vessels are intact. There is no vasculitis, no fibrinoid necrosis — so the overlying tissue is preserved and resolves without ulceration or scarring.[3]
Q2: Causes and the diagnostic search (3 min)
Examiner: What causes erythema nodosum?[1]
Candidate: It is a reactive dermatosis — a type IV hypersensitivity response to a remote antigen. The commonest identifiable cause in children is streptococcal pharyngitis. In adults I think of sarcoidosis (Lofgren syndrome), inflammatory bowel disease (Crohn more than UC), drugs (the oral contraceptive pill, sulphonamides), pregnancy, and other infections — TB, endemic fungi such as coccidioidomycosis and histoplasmosis, Yersinia, Chlamydia. About 30 to 50 percent remain idiopathic after a complete workup.[1]
Examiner (push): What is the minimum workup in every patient?[1]
Candidate: A chest X-ray, an ASO titre and throat swab, a careful drug history, a pregnancy test in any woman of reproductive age, and a CBC with ESR and CRP. Stool studies and an IBD screen follow GI symptoms. Biopsy is reserved for atypical, ulcerating or persistent lesions — and it must include subcutaneous fat.[1]
Q3: Lofgren syndrome (2 min)
Examiner: The chest X-ray shows bilateral hilar lymphadenopathy and her ankles are swollen. What is this and what do you do?[4]
Candidate: That is Lofgren syndrome — the triad of erythema nodosum, bilateral hilar lymphadenopathy and ankle arthritis. It is an acute presentation of sarcoidosis with an excellent prognosis. When the full triad is present the diagnosis is clinical — no biopsy is required. I manage with observation and NSAIDs for the arthralgia; it resolves within two years in most patients. HLA-DRB1*03 predicts a favourable outcome.[4]
Q4: Management and escalation (3 min)
Examiner: How do you manage her?[1]
Candidate: First, treat or remove the trigger — penicillin for confirmed strep, review the oral contraceptive pill. Symptomatic care: bed rest, leg elevation, and ibuprofen 400 mg three times daily for one to two weeks. If refractory, I escalate to potassium iodide 300 to 900 mg daily, colchicine 0.5 mg twice daily for recurrent disease, or hydroxychloroquine. A short course of systemic corticosteroid is last-line and I would exclude tuberculosis first.[1]
Examiner (push): Why exclude tuberculosis before steroids, and what cautions apply to potassium iodide?[7]
Candidate: Because corticosteroids can activate and disseminate latent TB — I perform an IGRA or Mantoux and a chest X-ray first. As for potassium iodide, it suppresses neutrophil chemotaxis in the septa, but it is contraindicated in pregnancy (fetal goitre) and can cause hypothyroidism via the Wolff-Chaikoff effect, so I monitor the TSH.[7]
Q5: The discriminator and prognosis (2 min)
Examiner: A colleague calls the calf nodules that are ulcerating "erythema nodosum." Do you agree?[3]
Candidate: No. Ulcerating nodules on the calves are not erythema nodosum — they are erythema induratum, nodular vasculitis. The comparison: EN is septal, on the shins, does not ulcerate, has no vasculitis, and is driven by strep, sarcoid or IBD; erythema induratum is lobular with vasculitis, on the calves, ulcerates and scars, and is TB-associated. The prognosis of EN is excellent — self-limiting, no scarring — whereas erythema induratum is chronic, relapsing and scars.[1][3]
References4Show ledgerHide ledger
- [1]Pérez-Garza DM, Chavez-Alvarez S, Ocampo-Candiani J, et al. Erythema Nodosum: A Practical Approach and Diagnostic Algorithm. American Journal of Clinical Dermatology, 2021.PMID 33683567
- [3]Wick MR. Panniculitis: A summary. Seminars in diagnostic pathology, 2017.PMID 28129926
- [4]Abdelghaffar M, Hwang E, Damsky W. Cutaneous Sarcoidosis. Clinics in chest medicine, 2024.PMID 38245372
- [7]Goel N, Doshi BR Potassium Iodide in Dermatology - Recent Advances in Mechanism of Action, Preparation, Uses and Adverse Effects. Indian journal of dermatology, 2025.PMID 40487487