In a narrative review in the American Journal of Kidney Diseases, Dr. Antoine Bouquegneau and colleagues discuss anorexia nervosa (AN) and the kidney. Electrolyte disorders and tubular damage is commonly associated with this entity. Drs. Antoine Bouquegneau (AB) and Pierre Delanaye (PD), both from University of Liege, Belgium, discuss their article with Kenar Jhaveri (eAJKD), eAJKD Blog Editor.
eAJKD: Can you give us the breakdown of various types of kidney diseases seen in AN?
AB: Glomerular lesions are not so prevalent. The typical glomerular findings are a nonspecific glomerulosclerosis and hyperplasia of the juxtaglomerular apparatus, reflecting a chronic hyper-reninemic state. Tubulointerstitial lesions usually appear as vacuolar lesions in epithelial cells of the proximal tubule, leading to an anthology of ionic disturbances: hypokaliemia and metabolic alkalosis. Disturbances of water homeostasis and nephrolithiasis are other types of kidney injuries observed in AN patients.
Table 2 and 3 in the article have summarized major complications seen with AN.
eAJKD: Why do significantly high number of patients (70%) with AN have some form of kidney disease.
PD: The prevalence of 70% of kidney disease in AN includes all types of kidney disturbances, including electrolyte disturbances, acute kidney injury, chronic kidney disease (CKD), nephrolithiases, and refeeding syndromes.
eAJKD: Of all the electrolyte abnormalities in AN, what do you think is the most dangerous and why?
PD: It is hypokalemia. Both acute and chronic hypokalemia have actually strong and potentially fatal consequences. Acute hypokalemia is principally due to volume depletion and repeated episodes of vomiting in binge-purging type of AN. Acute hypokalemia is very dangerous because of cardiac arrhythmias. Chronic electrolyte abnormalities are well correlated with definitive morphologic changes in renal tubules, and they are the largest cause of CKD in AN.
eAJKD: What could the renal community do to raise awareness of kidney disease in this population?
AB: Detecting kidney disease is important in this population both because it is very frequent and affects adolescents and young adults. It is associated with significant morbidity and mortality. It is also very important to underline the difficulties in diagnosing kidney diseases because commonly used methods to estimate GFR and measure proteinuria may be particularly misleading in patients with low body mass.
eAJKD: Can you explain why proteinuria is not that easy to measure in AN patients?
AB: The excretion of specific types of protein, such as albumin or low molecular weight globulins, depends on the type of kidney disease. In AN patients, tubulointerstitial disease is more prevalent than glomerular disease. Low molecular weight globulins (like cystatin C or β2-microglobulin) are sensitive markers for this type of tubulointerstitial diseases. This type of protein is not detected on urine dipstick testing. In clinical practice, the use of the urinary spot protein to creatinine ratio ensures that the urinary protein or marker is quantified according to the urinary concentration. In patients with AN, urinary creatinine excretion might be very low compared with patients without AN because of abnormally low muscle mass. Therefore, using the classical ratio can be falsely reassuring in these patients. In AN, we would recommend measuring proteinuria (and thus urinary cystatin C or β2-microglobulin) on a 24-hours urine collection.
eAJKD: What do you suggest is the best way to assess GFR in these patients?
PD: Using creatinine-based equations to estimate GFR is misleading and falsely reassuring in AN patients. Indeed, serum creatinine is also dependent of muscle mass, which is particularly low in AN patients. Using creatinine-based equation will thus logically overestimate true GFR. Therefore, creatinine clearance measurements in timed urinary collections is also useful. Measuring GFR by a reference method must be considered, eg, iohexol or iothalamate clearance. We are optimistic that newer kidney biomarkers may have high utility in this population.
eAJKD: Are these patients more non-compliant than other CKD patients given their AN history, and how do we best approach this as a CKD community?
PD: In our own experience, it is clear that compliance in AN is less than in other patients. We think that a multidisciplinary approach, notably with psychiatrists, is the best way to follow these patients. Patience and persuasive force are two qualities necessary in the care for these young patients. It must also be underlined that objectifying a somatic disease may be of some help (even if it is a bit contradictory!) from a psychological point of view in these patients who frequently deny their psychological disorder and distress.