Myxing It Together: An Uncommon Association?

Introduction Mixed cryoglobulinaemia syndrome (MCS) is a rare multisystem autoimmune disorder characterised by abnormal production of type II/III cryoglobulins, leading to immune complex−mediated small-to-medium vessel vasculitis. The vast majority of MCS are secondary to infections, namely, hepatitis C, along with autoimmune connective tissue and lymphoproliferative disorders. Paraneoplastic solid-tumour aetiologies are rare and only described in case reports. We present a case of MCS simultaneously diagnosed with a right-sided atrial myxoma and postulate an association between these two uncommon entities. Case Presentation A 31-year-old, previously healthy lady presented with acute dyspnoea and haemoptysis on the background of subacute small-joint arthralgia and bilateral lower-limb petechial rash. Computerised tomography pulmonary angiography revealed a large mass/thrombus within the right atrium/ventricle extending into the pulmonary trunk. Viral respiratory swab detected SARS-CoV-2. She rapidly deteriorated from hypoxic respiratory failure and was treated with thrombolysis/anticoagulation, intravenous dexamethasone, and surgical resection of the right-atrial mass, leading to rapid improvement. Histopathological analysis confirmed a cardiac myxoma. Skin biopsy of the petechial rash revealed leukocytoclastic vasculitis with a ‘full house’ immunofluorescence pattern. A mixed cryoglobulin was subsequently detected, securing a diagnosis of MCS. Subsequent investigations suggested renal involvement, but no neurological disease. Workup for blood-borne viruses, autoimmune connective tissue, and lymphoproliferative disorders did not reveal a definitive underlying aetiology. Treatment and Follow-Up In the absence of an alternative cause, we postulated that the MCS was a paraneoplastic phenomenon of the cardiac myxoma, with an acute flare precipitated by SARS-CoV-2 infection. The patient remained stable for two weeks post-myxoma resection and continues to be monitored without further treatment. The patient’s progress, subsequent management, and postulated immunopathological mechanisms will be presented. Conclusion We present a rare case of MCS concurrently diagnosed with a cardiac myxoma. This case adds to the sparse existing literature, suggesting a possible association between these two rare entities.