iatroX Rounds #45
The clues
- 1
A 32-year-old man presents to his GP reporting progressive weakness in his hands and difficulty performing tasks such as turning a key in a lock.
- 2
He describes a phenomenon where his muscles feel stiff, particularly in his hands, and he has trouble releasing his grip quickly after shaking hands or holding a shopping bag.
- 3
His family history is significant for his father having required a permanent pacemaker in his 40s and undergoing surgery for bilateral cataracts at a young age.
- 4
On examination, he has a distinct facial appearance with a high forehead due to frontal balding, bilateral ptosis, and a narrow, expressionless face.
- 5
Blood tests show a low serum testosterone and an elevated creatine kinase, while an ECG reveals first-degree heart block and a widened QRS complex.
- 6
Clinical examination reveals prominent wasting of the sternocleidomastoids and distal limb muscles, with a slow, sustained contraction of the thumb after the thenar eminence is tapped with a tendon hammer.
Myotonic dystrophy type 1 is an autosomal dominant multisystem disorder caused by a CTG trinucleotide repeat expansion in the DMPK gene on chromosome 19. It is the most common adult-onset muscular dystrophy and is characterised by progressive muscle wasting and the inability of muscles to relax after contraction.
- Distal muscle wasting and weakness affecting the hands and feet.
- Myotonia, which is a delay in muscle relaxation following a voluntary contraction or mechanical stimulation.
- Non-muscular features including frontal balding, cataracts, primary hypogonadism, and cognitive impairment.
- Cardiac conduction abnormalities that can progress to complete heart block or sudden death.
for education and entertainment. not medical advice.