Erythema Nodosum (EN) is the most common form of septal panniculitis, with over 100 reported infectious, malignant, inflammatory, idiopathic, and autoimmune causes.

A 41-year-old woman presented with a violaceous papule on the dorsum of the hand, large ipsilateral axillary lymphadenopathy, and tender, erythematous, subcutaneous nodules on the legs. Accompanying signs included fever, ankle swelling, and bilateral red eye. She recalled having a previous exposure to kittens one month before and had a positive family history for sarcoidosis. Histological examination of the hand lesion showed sarcoidal granulomas with positive Bartonella henselae DNA, whereas a biopsy done on the leg nodules was compatible with erythema nodosum. Cat scratch disease (CSD) typically presents as a tender regional lymphadenopathy preceded by an inoculation papule with spontaneous resolution occurring between 8-16 weeks. Cutaneous manifestations of CSD are rare, with erythema nodosum accompanying only 0.6% of cases. Although speculative, the background of a positive family history for sarcoidosis may explain the atypical presentation of this case, with red eye, persistent arthralgia, and associated sarcoidal granulomas.

Erythema nodosum (EN) is a form of septal panniculitis, which is believed to represent a delayed hypersensitivity reaction activated by infectious agents, drugs, granulomatous and autoimmune diseases, pregnancy, and malignancies. There are only four reported cases of EN during oral isotretinoin therapy to our knowledge, all of them occurring in patients with severe acne. Since acne itself can trigger EN, the question as to whether there is indeed a causative relationship between isotretinoin and EN in the reported cases remains to be elucidated. We present herein a 20-year-old woman with multiple vulvar condylomata acuminata who developed EN two weeks after onset of oral isotretinoin therapy. To the best of our knowledge, this is the first report of EN occurring during isotretinoin treatment in a patient without acne and strongly indicates that the pathogenesis of EN can be directly related to the biological actions of isotretinoin. Erythema nodosum should be regarded as a rare side effect of oral isotretinoin therapy, regardless of the underlying disease. Physicians should be aware of this rare side effect.

Erythema nodosum (EN) is associated with many systemic diseases and infections. This casereport provides an image of erythematous nodules, an overview of the various causes of EN, andthe laboratory tests and imaging that can be done in the emergency department to narrow its broaddifferential diagnosis.

Panniculitis, inflammation of the subcutaneous fat, is a relatively uncommon condition that usually presents with inflammatory nodules or plaques. Erythema nodosum (EN) is clinically the most frequent form of panniculitis and is considered a reactive process that may be triggered by a wide variety of stimuli. Whilst up to 55% of EN is considered idiopathic, the most common causes include infections, drugs, systemic illnesses such as sarcoidosis and inflammatory bowel disease, pregnancy, and malignancy. EN typically presents in the teens and 20s, and is seen more commonly in females. It is often preceded by a non-specific prodrome of one to three weeks, which may include fever, malaise, and symptoms of an upper respiratory tract infection. Cutaneous lesions then follow, typically localized on the extensor aspect of the limbs. The lesions are painful rounded or oval, slightly raised, non-ulcerative red nodules. The exact pathogenesis of EN is not understood, although is thought to result from deposition of immune complexes in the venules of the septae in subcutaneous fat, causing a neutrophilic panniculitis. The classical histopathological picture is of a septal panniculitis without vasculitis. However, the pathological features vary with the chronology of the lesions. Even without specific therapy for a causative condition, EN typically resolves without treatment. Therefore, symptomatic support is adequate for the majority of patients.

Reactive cutaneous coccidioidal skin manifestations are commonly noticed during the early stage of coccidioidomycosis. These skin lesions are devoid of any active coccidioidal organism, and the immune trigger mechanisms are not elucidated. We describe 6 cases of unusual reactive cutaneous coccidioidal manifestation, characterized by painful vesiculobullous lesions known as erythema sweetobullosum. The biopsy of the lesions revealed neutrophilic dermatosis with inflammatory cells resulting in a cleft and elevation of the most superficial layer of the skin forming a bulla. The reactive cutaneous lesion is self-limited and requires no specific therapy.

Lepromatous leprosy is associated with a high bacillary load and poor cellular immune response. Early dermatologic manifestations include erythematous macules, papules, nodules, and plaques with a symmetrical distribution. Leprosy also shows two major reaction states including type I (reversal reaction) and type II (vasculitis). These reactions are usually seen in some patients who are undergoing treatment. Herein, we report an interesting patient with lepromatous leprosy who presented with skin lesions of type II reaction without receiving any anti-leprosy treatment and surprisingly showed a type I reaction eight months after the beginning of the treatment.