Medical Mystery of the Week

Because of the COVID19 pandemic you are practicing telemedicine. You are presented a case of a 25-year old woman who presents with a chief complain of painful "lumps" on the front of her legs (see picture below). She denies any other symptoms and her past medical history is unremarkable. With the exception of the leg findings, her physical eamination is reported as normal. You are shown a PA and right lateral chest x-ray (see below). What is your diagnosis, what test(s) would you order to confirm your suspicions, and what treatment, if any, do you recommend?

DIAGNOSIS: Erythema nodosum (EN) secondary to primary pulmonary tuberculosis.

EN is a sepal panniculitis typically presenting with tender anterior tibial erythematous subcutaneous nodules. The lesions are usually bilateral and symmetrical, ranging from 1-5 cm in diameter. On occassion, EN may involve the anterior thighs and dorsum of the upper extremities. Patients may also experience polyarthragias. EN is associated with a multitude of diseases, including granulomatous diseases (tuberculosis, histoplasmosis, sarcoidosis, Behcets, Crohns disease, and Yersinia enterocolitis), Group A streptococcal infection, various medications (e.g., penicillins, sulfonamides), pregnancy, vaccinations, and even with the use of copper IUDs. About 50% of cases are idiopathic. Treatment of EN is supportive and may include nonsteroidal antiiflammatory agents and low dose short-term glucocorticoids. EN can evolve into a chronic disorder. Primary pulmonary tuberculosis is an infection in a naive (tuberculin negative) host. Often asymptomatic, the primary site of infection may be a Gohn complex, a segmental infiltrate, or an atypical pneumonia with reactive lymphadenopathy in the hilum on the ipsilateral side (see right sided-hilar adenopathy and infiltrate in the superior segment of the right lower lobe in the x-ray above). Patients will have a positive PPD, but sputum and gastric samples will have have few or no organisms. Patients should be placed on prophylactic isoniazid. The appearance of primary pulmonary histoplasmosis may be identical to that seen in the presented case. In contrast to primary pulmonary infection with tuberculosis and histoplasmosis, sarcoidosis causes diffuse bilateral increases in interstitial markings and bilateral hilar adenopathy.