Pain or Weakness? An Immunocompromised Patient Presenting with Inability to Walk

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IntroductionErythema nodosum (EN) appears as tender erythematous nodules, mainly on the pretibial areas. The causes are varied including medication side effects, infections, autoimmune conditions, malignancy, and is idiopathic in 50% of cases. The pathophysiology is not completely understood but may involve an immunologic response or hypersensitivity reaction to various stimuli, leading to immune complex deposition in the venules of septae in subcutaneous fat. Case Presentation17-year-old male with right mandible ameloblastoma (positive for BRAF V600E mutation), who was diagnosed in May 2022, and has been semi-compliant with dabrafenib, BRAF V600E mutation kinase inhibitor, for the previous 6 months and was off for about 1 week when he presented with fever, followed by painful rash of extremities, including soles and palms, and ascending weakness with inability to walk, concerning for neurological insult. The rash was confluent, macular patches, non-pruritic, blanching with a needle-like tenderness. We questioned whether the inability to walk was neurological or related to pain. Brain Magnetic Resonance Imaging (MRI) was unremarkable. Extensive infectious disease testing yielded rhinovirus/enterovirus positive Polymerase Chain Reaction (PCR) but was negative for all other pathogens, including Streptococcus A infection. Rheumatologic workup was negative. He was treated with Non-Steroidal Anti-Inflammatory Drugs and triamcinolone cream which provided improvement of rash and presenting symptoms. Skin biopsy showed granulomatous panniculitis compatible with EN. Dabrafenib was discontinued. DiscussionPatient’s initial presentation was concerning for acute onset of ascending weakness in an immunocompromised patient, suggestive of Guillain-Barré syndrome. Muscular strength was difficult to examine upon initial physical exam likely due to patient effort versus experienced symptoms and patient’s need for assistance to ambulate. However, detailed neurological examination and having normal brain MRI led to the conclusion that the acute change was EN-related pain, rather than weakness. After extensive infectious and rheumatological work up, we concluded that the patient’s EN was likely secondary to Dabrafenib use even if adherence was suboptimal. Clinicians should be aware that EN is an adverse reaction which has been reported in relation to Dabrafenib, as evidenced by a retrospective chart review and case report.