Catastrophic antiphospholipid syndrome (CAPS) is a life-threatening form of antiphospholipid syndrome characterised by diffuse arterial and venous thrombosis, in the presence of positive antiphospholipid antibodies. The multiple sites of thrombosis in small, medium and large vessels progress to multiorgan failure, accounting for the high mortality rate associated with CAPS. Unregulated complement activation is increasingly recognised as critical to the pathogenesis of CAPS. Early diagnosis is essential to initiate prompt life-saving treatment with the triple therapy of anticoagulation, immunosuppression and either plasmapheresis or intravenous immunoglobulin. Among other immunosuppressive agents, eculizumab, a complement inhibitor has demonstrated efficacy in treatment-resistant cases.We report an instructive case of a woman presenting with both clinical and laboratory findings consistent with primary CAPS, resistant to initial treatment and responsive to eculizumab, with emphasis on genetic testing and implications for future therapy.

Complement-mediated kidney disease has been an evolving area in the field of nephrology. Atypical haemolytic uraemic syndrome (aHUS) is a rare thrombotic microangiopathy that affects multiple organs, particularly kidneys. The disease is characterised by a triad of haemolytic anaemia, thrombocytopenia and acute kidney injury (AKI). aHUS is most commonly caused by dysregulation of alternative complement pathway. In contrast to shiga toxin-associated haemolytic uraemic syndrome, diarrheal prodrome is usually absent in children with aHUS. We report a 2-year, 9-month-old boy who presented with acute dysentery and AKI. He had an unusual prolonged course of illness with hypocomplementaemia; hence, genetic testing was performed. He had a storming course in the hospital and succumbed to complications of the disease. Genetic study revealed digenic mutation in Complement Factor I and C3 Therefore, it is important to differentiate aHUS from other thrombotic microangiopathies to improve the outcome.

Renal angiomyolipomas (AMLs) were first described in the early 1900s by Gravitz, but it was not until 1951 that they were named renal AML. These kidney tumours are rare, occurring in 0.13%-0.44% of the population. These mesenchymal tumours are composed of smooth muscle-like, adipocyte-like and epithelioid cells. Depending on the predominant cell population, it can be further subclassified into classic, epithelioid and AML with epithelial cyst. A 32-year-old woman presented with mild, intermittent, epigastric and right upper quadrant abdominal pain. Abdominal ultrasound revealed an incidental lesion within the inferior vena cava (IVC). A CT scan showed a lesion within the left renal vein extending into the IVC with 40% narrowing and a fat-containing mass in the lower pole of the left kidney of 15 mm suggesting an AML. Thrombectomy was performed. The specimen resulted positive for classic variant renal AML. Initial diagnosis is centred on imagining studies, based in fatty tissue concentration. The AML expresses melanocytic markers. This helps differentiate from renal cell carcinoma. Although AML is considered a benign condition, there is evidence of malignant transformation. Active surveillance is recommended for lesions <4 cm. Nephron sparing surgery is the procedure of choice. Nephrectomy is recommended if there is a high probability of malignancy. Mammalian target of rapamycin (mTOR) inhibitors have been proposed to be an alternative treatment.

Falsely elevated potassium levels are common in routine laboratory tests and should be differentiated from true hyperkalemia. If the patient is inappropriately treated for hyperkalemia, the resulting hypokalemia can lead to life-threatening cardiac arrhythmias. We present the case of a 67-year-old woman with a past medical history of stable chronic lymphocytic leukemia, who presented for chest pain and had an elevated potassium level of 5.8 mEq/L, which, upon repeat laboratory testing, was then 6.7 mEq/L. She was initially treated for hyperkalemia. Laboratory test results showed creatine kinase levels at 43 U/L, lactate dehydrogenase levels at 177 U/L, phosphorus levels at 4.5 mg/dL, and uric acid levels at 6.4 mg/dL, indicating no evidence of tumor lysis syndrome. The patient was later diagnosed with reverse pseudohyperkalemia, indicated by falsely elevated plasma potassium levels in the presence of serum potassium levels within normal limits and venous blood gas samples.

Pyomyositis is considered a great mimicker and masquerader. This case is of a 63-year-old man with diabetes who initially presented to the outpatient clinic afebrile with right shoulder pain. His work-up was negative, and he was discharged home. He subsequently presented to the emergency room (ER) two times for worsening right shoulder pain. During his first visit to the ER, his work-up was unremarkable, and he was discharged home. On his return to the ER, he was now febrile with inflammation involving his right upper extremity and right chest wall. Imaging studies of his right upper extremity and his right chest wall were consistent with multiple abscesses. Methicillin resistant Staphylococcus aureus was cultured from the abscess, and from blood and urine cultures. The diagnosis of pyomyositis was confirmed. This case illustrates the difficulty of diagnosing pyomyositis and the importance of including it in the differential diagnosis, especially in an immunocompromised patient.

Kidney transplant recipients have been reported at a particularly high risk of severe COVID-19 illness due to chronic immunosuppression and coexisting conditions. Yet, here we describe a remarkably mild case of COVID-19 in a 62-year-old female who had a kidney transplantation 10 years earlier due to autosomal dominant polycystic kidney disease. The patient was admitted for 1 day; immunosuppressive therapy with tacrolimus and low-dose prednisolone was continued; and the patient recovered successfully without the use of antiviral agents or oxygen therapy. The case demonstrates that kidney transplant recipients are not necessarily severely affected by COVID-19. Withdrawal of immunosuppressive therapy could be associated with poorer outcomes and should not be implemented thoughtlessly.

This is an educational case suitable for all readers, but aimed particularly at trainees preparing for MRCP. Using the example of a patient presenting to clinic with proteinuria, aspects of differential diagnosis, pathology and management are explored.

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