In the intricate world of medical diagnoses, sometimes the most perplexing cases hold the most surprising revelations. Take, for instance, the recent encounter of a 72-year-old gentleman who came knocking on the doors of healthcare with a barrage of symptoms that left both him and his caregivers scratching their heads.

This gentleman, a known case of hypertension and ischemic heart disease with a history of a past percutaneous transluminal coronary angioplasty (PTCA) in 2011, presented a clinical puzzle that took some unraveling. His laundry list of complaints included a low-grade fever lingering for a week, a persistent cough, leg pain, intermittent vomiting, confusion, weight loss, and loss of appetite. Quite the ensemble of symptoms, wouldn't you agree?

Upon clinical examination, the picture became clearer, yet more confounding. He had a thin build, unremarkable vital signs except for a recurrent hyponatremia, and itchy, scaly skin lesions adorning his left forearm. Auscultation revealed few crepitations over his right infra-clavicular and mammary area, adding another layer to the diagnostic conundrum.

Laboratory investigations, while mostly unremarkable, highlighted the persistent recurrence of hyponatremia, a perplexing mystery that begged for resolution. Despite meticulous probing into potential causes, including a detailed evaluation for hyponatremia and even attributing it to a nutritional deficiency, no conclusive answers emerged. Even after six months of relentless symptomatology and two hospital admissions, there was no clinical or laboratory improvement to speak of.

As the investigative journey continued, further tests were ordered. Sputum smears and cultures returned negative for acid-fast bacilli (AFB), ruling out pulmonary tuberculosis initially. However, a twist in the tale emerged when gene Xpert testing came back positive for AFB. Subsequent cultures on Sabouraud Dextrose Agar (SDA) revealed the presence of dimorphic fungi, later identified as Blastomyces dermatitidis through sequencing. 

The final diagnosis? Tubercular mediastinal lymphadenopathy, a rare manifestation of extrapulmonary tuberculosis (EPTB) that had been masquerading behind the veil of recurrent hyponatremia. With the diagnosis in hand, the patient was promptly started on a multidrug therapy regimen (HRZE), and to the relief of all involved, his hyponatremia gradually resolved, signaling a path to recovery. 

This case underscores several important lessons. Firstly, it highlights the importance of considering uncommon etiologies in patients with recurrent hyponatremia, especially in the context of persistent symptoms and lack of improvement despite conventional management. Secondly, it underscores the necessity of a multidisciplinary team (MDT) approach in tackling complex medical cases, where input from various specialties can shed light on the darkest corners of diagnostic dilemmas. 

Moreover, the case demonstrates the efficacy and safety of advanced diagnostic tools such as endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) in unmasking mediastinal pathology. In this instance, EBUS-TBNA played a pivotal role in obtaining tissue samples for definitive diagnosis, ultimately guiding appropriate management and improving patient outcomes. 

In conclusion, while medical mysteries may confound and perplex, they also offer invaluable opportunities for learning and discovery. By embracing a holistic approach to patient care and leveraging cutting-edge diagnostic modalities, healthcare providers can navigate even the most labyrinthine of cases, ultimately leading to better outcomes and improved patient well-being.