4th March 2024

A 16-year-old male presents to the neurology clinic with a 6-month history of worsening ptosis

A 16-year-old male presents to the neurology clinic with a 6-month history of worsening ptosis and diplopia. He also notes that he has had difficulty seeing in the dark for the past three months. He is known to have sensorineural hearing loss and hypothyroidism. Examination today reveals a limitation to gaze in all directions. Bilateral ptosis is also noted. Fundoscopy reveals pigmentary changes within the peripheral fundus with a bone-spicule appearance. An ECG was performed, and this showed a right bundle branch block with a left anterior fascicular block. Blood tests show an elevated lactate. CSF samples show raised levels of proteins and lactate.

What is the likely underlying diagnosis?

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