Dermatology · Panniculitis
The facts most likely to be tested
Erythema nodosum presents as painful, erythematous, tender nodules typically located on the anterior shins.
Histopathology reveals septal panniculitis without primary vasculitis.
The most common infectious trigger is Streptococcus pyogenes (Group A Strep) pharyngitis.
Erythema nodosum is a classic extraintestinal manifestation of Inflammatory Bowel Disease (specifically Crohn disease).
Sarcoidosis is a high-yield systemic cause, often presenting with bilateral hilar adenopathy on chest X-ray.
Drug-induced cases are frequently associated with oral contraceptives, sulfonamides, and penicillins.
Initial management focuses on NSAIDs for pain control and treating the underlying systemic etiology.
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A 28-year-old woman presents to the clinic with a 1-week history of painful, red, raised nodules on her bilateral anterior shins. She reports recent episodes of bloody diarrhea and abdominal cramping. Physical examination reveals tender, indurated, erythematous plaques that are warm to the touch. A chest X-ray is performed and shows no hilar adenopathy.
What is the most likely underlying diagnosis for this patient's skin condition?
Crohn disease
The patient's presentation of tender pretibial nodules is classic for erythema nodosum, which is strongly associated with inflammatory bowel disease, particularly Crohn disease.
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High yield triage
Etiology / Epidemiology
Common in females 20-40 years old; triggered by streptococcal infection, sarcoidosis, or oral contraceptives.
Clinical Manifestations
Painful, tender red nodules on the anterior shins; panniculitis without ulceration.
Diagnosis
Clinical diagnosis; incisional biopsy if uncertain showing septal panniculitis.
Treatment
NSAIDs for pain; treat underlying trigger; avoid systemic steroids unless infection ruled out.
Prognosis
Self-limiting; usually resolves in 3-6 weeks without scarring.
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Epidemiology & Etiology
Most common form of panniculitis, frequently idiopathic or secondary to immune-mediated triggers. Primary associations include streptococcal pharyngitis, sarcoidosis, tuberculosis, and inflammatory bowel disease. Medications like oral contraceptives and sulfonamides are classic triggers.
Pertinent Anatomy
Involves the septal fat of the subcutaneous layer. The predilection for the pretibial area is due to the high concentration of adipose tissue and dependent venous stasis in the lower extremities.
Pathophysiology
A delayed-type hypersensitivity reaction (Type IV) to various antigens. Immune complexes deposit in the septal venules, triggering an inflammatory cascade. This results in the characteristic tender, indurated nodules without primary vasculitis.
Clinical Manifestations
Presents as bilateral, painful, erythematous nodules on the anterior shins. Lesions are non-ulcerative and evolve from bright red to a bruised, bilateral appearance. Systemic symptoms like fever, arthralgia, and malaise are common prodromal signs.
Diagnosis
Diagnosis is primarily clinical. If the presentation is atypical, an incisional biopsy is the gold standard to confirm septal panniculitis without vasculitis. Order CXR to rule out Löfgren syndrome (sarcoidosis).
Treatment
Management focuses on identifying and treating the underlying cause. NSAIDs are the first-line therapy for symptomatic relief. Systemic corticosteroids are contraindicated unless an infectious etiology is definitively excluded.
Prognosis
The condition is typically self-limiting, with lesions resolving spontaneously within 3-6 weeks. Recurrence is possible if the underlying trigger is not addressed or if the patient remains on the offending medication.
Differential Diagnosis
Erythema induratum: involves posterior legs and ulceration
Cellulitis: usually unilateral and associated with warmth/lymphangitis
Polyarteritis nodosa: associated with systemic vasculitis and livedo reticularis
Septic thrombophlebitis: palpable cord-like vein
Traumatic contusion: history of trauma and lack of systemic symptoms