Descending Guillain-Barré Syndrome Presenting as Bilateral Phrenic Nerve Palsy.

Bilateral phrenic nerve palsy is a rare and potentially life-threatening cause of respiratory failure, particularly when occurring in young, otherwise healthy individuals without identifiable risk factors. We report a case of a 32-year-old male presenting with acute-onset orthopnoea following a brief history of bilateral shoulder pain. Clinical examination revealed paradoxical abdominal breathing, and imaging demonstrated elevated hemidiaphragms with markedly reduced diaphragmatic excursion, suggestive of diaphragmatic dysfunction. Extensive evaluation excluded common causes including pulmonary, structural cervical, neuromuscular junction, and toxic aetiologies. Nerve conduction studies, cerebrospinal fluid analysis, and autoimmune markers were non-contributory. Despite inconclusive investigations, the progressive respiratory compromise and clinical pattern raised suspicion for an atypical immune-mediated neuropathy, likely a descending variant of Guillain-Barré Syndrome presenting as isolated bilateral phrenic nerve palsy. The patient showed no improvement with corticosteroids and required intermittent non-invasive ventilation. Due to financial constraints, plasmapheresis was initiated, resulting in significant clinical recovery and complete resolution of symptoms. This case underscores the importance of early recognition of diaphragmatic weakness and reliance on clinical judgment in atypical presentations. Prompt empirical treatment can be life-saving, even in the absence of definitive diagnostic confirmation.