title: Value of Renal Biopsy in Diagnosing Infantile Nephropathic Cystinosis Associated With Secondary Nephrogenic Diabetes Insipidus.
abstract: Cystinosis is the most common cause of inherited renal Fanconi syndrome in young children, and typically presents with laboratory findings of a proximal tubulopathy and corneal crystals by one year of age. We describe here renal biopsy findings in a 20-month-old patient with an atypical presentation of distal renal tubular acidosis, diabetes insipidus, and the absence of corneal crystals. Although renal biopsy is usually not necessary to establish the diagnosis of cystinosis, when the patient presents with atypical signs and symptoms, a renal biopsy may be extremely valuable. A 20-month-old boy presented with failure to thrive, polyuria, polydipsia, and rickets. He initially showed evidence of a renal tubular acidosis, mild renal insufficiency, and nephrogenic diabetes insipidus. His initial ophthalmologic examination did not demonstrate corneal crystals. His subsequent workup revealed phosphaturia, suggesting a partial proximal tubulopathy. Concomitantly, a renal biopsy revealed prominent podocytes with an immature glomerular appearance, and electron microscopy analysis showed numerous intracellular crystals within tubular epithelial cells. Subsequent laboratory and genetic testing confirmed a diagnosis of infantile nephropathic cystinosis. This case highlights the variability in the clinical presentation of cystinosis, resulting in an uncommon clinical picture of a rare disease. Given that treatment is available to prolong renal function and minimize the extra-renal manifestations of this disorder, early diagnosis is essential. It is important to raise the index of suspicion of cystinosis by recognizing its subtle morphological changes in young patients, and that nephrogenic diabetes insipidus can be secondary to this disorder.
authors.affiliation: 1 Division of Nephrology, Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Emily
authors.initials: E
authors.lastname: Joyce
authors.affiliation: 1 Division of Nephrology, Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Ho
authors.affiliation: 2 Division of Medical Genetics, Department of Pediatrics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Areeg
authors.initials: A
authors.lastname: El-Gharbawy
authors.affiliation: 3 Division of Pediatric Pathology, Children's Hospital of Pittsburgh of UPMC, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Cláudia M
authors.initials: CM
authors.lastname: Salgado
authors.affiliation: 3 Division of Pediatric Pathology, Children's Hospital of Pittsburgh of UPMC, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Sarangarajan
authors.initials: S
authors.lastname: Ranganathan
authors.affiliation: 3 Division of Pediatric Pathology, Children's Hospital of Pittsburgh of UPMC, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania, USA.
authors.forename: Miguel
authors.initials: M
authors.lastname: Reyes-Múgica
mesh_terms: D001706:Biopsy; D003554:Cystinosis / Q000150:complications / Q000175:diagnosis* / Q000473:pathology; D018500:Diabetes Insipidus, Nephrogenic / Q000175:diagnosis / Q000209:etiology*; D006801:Humans; D007223:Infant; D007668:Kidney / Q000473:pathology*; D008297:Male
keywords: cystine crystals; cystinosis; diabetes insipidus; electron microscopy; fanconi; nephropathic; renal biopsy