skip to main content

Adult Cystinosis Cysteamine Corneal Crystals — ESENeph MCQ

Instant feedback + full explanation. One question, done properly.

HardTubular DisordersAdult Cystinosis Cysteamine Corneal CrystalsESENeph

A 35-year-old woman presents with proximal muscle weakness, polyuria, and bone pain. Bloods: K+ 3.0 mmol/L, phosphate 0.55 mmol/L, bicarbonate 16 mmol/L, glucose normal. Urine: glycosuria (normoglycaemic), elevated beta-2-microglobulin, aminoaciduria, phosphaturia. She has corneal cystine crystals on slit lamp examination. eGFR is 40 mL/min/1.73m2. What is the specific pharmacological treatment for the underlying condition?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: A — Oral cysteamine (cystine-depleting agent)

Corneal cystine crystals are pathognomonic of cystinosis — confirming the diagnosis in a patient with Fanconi syndrome and progressive CKD. Oral cysteamine (Cystagon or Procysbi) is the specific treatment: it enters lysosomes, reacts with cystine to form a mixed disulphide (cysteine-cysteamine), which exits via the lysine transporter, thereby depleting lysosomal cystine. Cysteamine delays but does not prevent CKD progression when started early. It is required lifelong, including post-transplant (to prevent cystine deposition in other organs — thyroid, muscle, pancreas, CNS). Cysteamine eye drops are needed separately for corneal crystals (systemic cysteamine does not reach the avascular cornea). Supportive treatment of Fanconi syndrome (phosphate, bicarbonate, potassium replacement) is also essential.

Reference: Nesterova & Gahl 2017 – Cystinosis Treatment; NICE 2017 – Cysteamine