Failure to Thrive With Severe Hypokalemia Yields Cystinosis Diagnosis in a 19-Month-Old Female Child: A Case Report.

Cystinosis is a rare, genetically inherited disease that affects lysosomal storage of cysteine. It is the most common cause of Fanconi syndrome. Mutations have led to early-onset end-stage renal disease as well as other systemic organ failures. In this case, we report a 19-month-old female child who presented acutely to the outpatient clinic with nausea, vomiting, and diarrhea. The patient was previously diagnosed with unspecified renal tubular acidosis and treated with oral electrolytes. Early labs during her acute presentation showed severe hypokalemia and electrolyte imbalance, which necessitated a transfer to a pediatric ICU. Through confirmatory testing, a diagnosis of cystinosis was made. This case is an example of the recognition and treatment of a rare inherited disease.