Use of 99m Tc DMSA Scintigraphy in Assessment of Renal Complications of COVID-19

COVID-19 mainly affects respiratory and immune systems, but other organs like renal, cardiovascular, lung and nervous systems could also be involved in both acute and chronic settings (1, 2). There is a lot of studies that demonstrate an increasing number of long COVID-19 who continue to experience persistent symptoms weeks or even months after the initial disease. Reports suggested that 66-87% of COVID-19 patients have at least one persistent chronic symptom related to the disease, the most common symptoms are fatigue, cough, anosmia, headaches, arthralgia, and chest pain that affect those with all grades of COVID-19 as well as inpatients and outpatients (3). Nowadays, imaging departments worldwide are exploring the different ways to may help for the management of chronic long covid-19 (4). One of the important complications with high morbidity and mortality is renal involvement. Studies show that 5–23% of people with COVID-19 have the symptoms of acute kidney injury (AKI) including proteinuria, elevated blood urea and creatinine, hematuria,  and histopathological damages (5). The multiorgan invasion of SARS-CoV-2 is a result of the wide distribution of angiotensin-converting enzyme 2 (ACE2) receptors in the organs; kidneys have the highest expression of ACE2 receptors in the body. Mesangial cells, podocytes, parietal epithelium of the Bowman’s Capsule, and the collecting ducts in the kidney show ACE2 receptors. Several mechanisms have been proposed for the renal manifestations of COVID-19 including direct viral invasion to the kidneys as well as a disturbance in renin-angiotensin-aldosterone system (RAAS) homeostasis (6). This virus binds to ACE2 receptors and leads to systemic inflammation and immune dysregulation in different organs (7, 8). This invasion leads to renal complications of COVID-19 which are acute renal injury and also deterioration and progression of previous renal disease in chronic kidney disease (CKD) patients (9). A large number of patients after acute renal injury of COVID‐19 have typically experienced long-term renal consequences during follow‐up (5). Recent studies showed that the development of AKI is associated with a poor prognosis. Renal injury increases morbidity and mortality, therefore subjects with evidence of renal involvement should be closely monitored and appropriately managed to avoid any decline in renal function (10). Renal injury is common in moderate to severe SARS-CoV-2 patients. Baseline proteinuria is an independent risk factor for increased hospitalization duration and ICU admission in subjects with COVID-19 (11). Nuclear medicine as functional, anatomical, and molecular imaging could be useful in diagnosing chronic renal complications, follow up and evaluation of response to treatment (4). The purpose of this study is to introduce 99m Tc DMSA renal scintigraphy as a nuclear medicine imaging that proved to be accurate and sensitive in assessing the onset, progression, and response to treatment of cortical renal dysfunction of COVID-19 patients (12). 99m Tc-DMSA scintigraphy is a radionuclide scan that uses dimercaptosuccinic acid (DMSA) in assessing renal morphology, structure, and function. Radioactive technetium-99m is combined with DMSA and injected into a patient, followed by imaging with a gamma camera after 3 hours (13). Imaging time is approximately 5 - 10 minutes depending on the counts collected per view take. Usually, posterior and posterior oblique views are the best images for interpretation of the scan. The patient is asked to maintain good hydration before and after the radiotracer injection. Usually, fasting is not required for scans (14). 99m Tc-DMSA scintigraphy is a safe, widely available with a low radiation dose that provides information about the morphology and function of the cortex of kidneys utilizing radiopharmaceuticals with high renal clearance. It can also use for measuring relative renal function. Anatomical abnormalities causing renal vascular or urinary tract malfunction can be diagnosed as well (13). 99m Tc-DMSA scintigraphy could help in the evaluation of cortical dysfunction and relative function of kidneys. It can also be used for detection of focal renal parenchymal abnormalities, differential diagnosis of scar from recoverable cortical dysfunction 6 months after acute infection, detection of acute pyelonephritis, evaluation of response to therapy by comparing baseline and fallow up scans, and discovery of associated abnormalities: abnormal duplex kidney, small kidney, dysplastic tissue and horseshoe kidney (13). The number, size, and location of areas of cortical loss can be assessed as well (4). A large polar hypoactive area, without deformity of the outlines and with indistinct margins will generally heal; marked localized deformity of the outlines or deformed outlines (volume loss) generally correspond to permanent sequelae. Renal sequelae should anyway best be estimated on a DMSA scintigraphy performed at least 6 months after acute infection (15). In conclusion, review of articles show that 99m Tc DMSA cortical renal scintigraphy can use in renal complications of covid-19 by demonstrating acute cortical dysfunction, acute pyelonephritis, size of kidneys, and relative function of kidneys. In a chronic setting, we can use a DMSA scan for detection of cortical scars, progression of renal cortical dysfunction, and response to therapy. Further research is needed to help improve effectiveness of this imaging.