Unmasking Extrapulmonary Tuberculosis: The Diagnostic Conundrum of Erythema Nodosum in a Young Woman

Sir, A 20-year-old female with no significant past medical history presented with a 1-month history of intermittent fever (maximum temperature 101°F), malaise, loss of appetite, holocranial headache, and loose stools. There was no history suggestive of any localization and no history of recent travel. She was vaccinated as per the national guidelines and had a normal menstrual history. On physical examination, she was febrile, tachycardic, and normotensive. She had bilateral pitting pedal edema extending up to one-third of the tibial length. No lymphadenopathy, hepatosplenomegaly, or skin lesions were noted. The rest of the examination was unremarkable. Upon further inpatient workup, her initial laboratory investigations revealed a normal complete blood count, serum electrolytes, liver function tests, and renal function tests. Her chest radiograph and abdominal ultrasonography were normal. She was worked up for tropical fevers which came back negative. Baseline two-dimensional echo was normal. Viral markers were nonreactive. She had raised inflammatory markers and the Mantoux test was positive. A summary of relevant investigations is displayed in Table 1. With a working diagnosis of tropical fever in mind with culture reports awaited, she was started on broad-spectrum antibiotics including injection ceftriaxone and tablet azithromycin.Table 1: Investigation profileOn the 5th day of admission, she developed nodular, hyperpigmented, erythematous, and tender lesions measuring about 2–3 cm in diameter on the anterior aspects of both lower legs [Figure 1]. A clinical diagnosis of erythema nodosum (EN) was made and an autoimmune panel was ordered which came back negative. A computed tomography scan of the chest was performed, which showed enlarged necrotic mediastinal lymph nodes, the largest measuring 4.4 cm ×2.8 cm in the perivascular region. An endobronchial ultrasound-guided fine needle aspiration of the mediastinal lymph nodes was done and the cytology was positive for Mycobacterium tuberculosis (TB). GeneXpert and acid-fast bacilli were seen in the fine needle aspiration cytology sample. The patient was diagnosed with extrapulmonary TB with EN as a cutaneous manifestation. She was started on a four-drug antitubercular regimen (isoniazid, rifampicin, pyrazinamide, and ethambutol) and all other antimicrobials were stopped. She responded well to the treatment, with the resolution of fever within 7 days, resolution of the rash and pedal edema within 10 days. She was discharged and was followed up at the outpatient clinic. After 1 month’s visit, she was afebrile and had a resolution of symptoms. Our case had no cough, weight loss, or night sweats but had presented with loose stools. This nonspecific presentation made us manage the patient on a working diagnosis of underlying tropical infection, likely enteric fever. However, she had no response to antibiotics and had no reduction in the fever spikes. The appearance of EN shifted our focus to look out for specific causes including latent/extrapulmonary TB. EN is a type of septal panniculitis that presents as tender, erythematous nodules on the lower extremities, usually accompanied by systemic symptoms such as fever, malaise, and arthralgia.[1] However, the diagnosis of TB-associated EN can be challenging, as the clinical and radiological manifestations of TB may be subtle or absent. EN may be the first or the only clue to the diagnosis of TB in some cases.[2] Therefore, it is important to consider TB as a possible cause of EN, especially in endemic areas or in patients with risk factors for TB, such as immunosuppression, malnutrition, or contact history. This emphasizes the traditional methods upheld in clinical practice, where thorough physical examination of patients is essential for identifying diagnostic clues and signs crucial for reaching a definitive diagnosis.Figure 1: Erythema Nodosum rash over the anterior aspect of bilateral legs of our patientDeclaration of patient consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.