Elevated Procalcitonin Levels can Occur in Bacterial Infections and also in Medullary Thyroid Carcinoma.

Medullary thyroid carcinoma (MTC) is a rare and challenging type of thyroid cancer originating from parafollicular cells (C cells) that produce calcitonin. Diagnosing and monitoring this carcinoma can be complex due to its unique biomarkers. Procalcitonin (PCT), a precursor of calcitonin, and carcinoembryonic antigen (CEA) are important markers for MTC. Elevated PCT levels, particularly when they remain high post-infection treatment, and elevated CEA levels are significant indicators for suspecting MTC. This report emphasises the diagnostic and prognostic importance of these biomarkers in MTC, highlighting their roles in detecting and monitoring disease progression. Integrating PCT and CEA measurements into routine clinical practice can enhance detection, provide understanding of therapeutic responses and aid in the effective management of MTC. LEARNING POINTS: Procalcitonin (PCT) is a more stable and reliable biomarker than calcitonin for diagnosing and monitoring medullary thyroid carcinoma (MTC).Elevated carcinoembryonic antigen (CEA) levels effectively monitor MTC progression, especially when calcitonin levels are inconsistent.Incorporating PCT and CEA measurements into routine practice enhances MTC management, providing reliable biomarkers for diagnosis and monitoring.

A Rare Post-Infectious Autoimmune Manifestation of COVID-19.

The incidence of post-infectious autoimmune diseases has been on the rise following the COVID-19 pandemic. Recently, an autistic patient was admitted to the hospital presenting with a mild upper respiratory system COVID-19 infection. Months after recovery and polymerase chain reaction negativity, the patient developed HEp-2 cell positivity and presented with relapsing polychondritis (RP), a rare autoimmune disease. The mechanism of this autoimmune invasion is ultimately caused by activating a myriad of immune reactions. Lymphocytopenia almost always accompanies various clinical forms of COVID-19; however, it may drive the lymphocytopenia-induced proliferation of autoreactive T cells via the activation of interleukin-6 (IL-6). Moreover, high levels of neutrophils during infection promote autoimmune disease by releasing cytokine and chemokine cascades that accompany inflammation, and neutrophil extracellular traps regulating immune responses through cell-cell interactions. Furthermore, autism spectrum disorder patients display an altered immune system that includes an augmented inflammatory cytokine milieu leading to an increased pro-inflammatory Th1/Th2 ratio. In addition, the pathophysiology of RP is majorly associated with a cell-mediated immune reaction; thus, the predisposing exaggerated immune system of such patients must also be considered as a predisposing factor to the development of post-infectious autoimmune diseases. LEARNING POINTS: COVID-19 infection is a potential trigger for relapsing polychondritis, an autoimmune disease affecting cartilage, and must be considered as a rare post-COVID complication.The hyperactive immune system in autism spectrum disorder (ASD) is an important predisposing factor to the induction of more autoimmune diseases after the occurrence of post-infectious dysregulation.Lymphocytopenia-induced proliferation possibly initiates the post-infection immune dysregulation.