Thread by @LyellJ

Solving the Case of the Vanishing Leg:

“My right leg is disappearing.”

➡️ 48 years old
➡️ Whole right lower limb weakness, atrophy
➡️ Progressive
➡️ Painless

What’s going on? 🧵1/8

As always, start with the patient (before the data). Where does this localize?

Weakness and atrophy often localize to nerve (motor neuron especially when no sensory symptoms)

➡️ BUT, some asymmetric myopathies can present similarly

Simple rubric to localize weakness: 2/8

https://twitter.com/LyellJ/status/1392906522594848768

Imaging was performed with a concern for multiple radiculopathies.

MRI showed no structural root lesions. But is it normal? 3/8

Diffuse T2 prolongation and T1 shortening in paraspinal muscles suggests an axial myopathy

➡️ Chronic replacement of muscle with adipose/connective tissue 4/8

EMG in these cases can be extremely helpful. 🔈

Rather than the large motor unit potentials (MUPs) that would be expected in ALS, radiculopathies, or plexopathy, the MUPs are

➡️ Short duration
➡️ Low amplitude
➡️ Complex

In other words, suggestive of myopathy… but which? 5/8

Most myopathies are diffuse, proximal, and symmetric. But there’s no shortage of strange patterns or asymmetries:

➡️ IBM
➡️ Dysferlinopathy
➡️ Anoctamin 5
➡️ Dystrophinopathy heterozygotes
➡️ and in our patient…

Facioscapulohumeral muscular dystrophy (#FSHD, nice job @NotoriousEMG!)

➡️ Common dystrophic myopathy
➡️ D4Z4 deletions (most)
➡️ Fascinating genetic mechanism and story…

pubmed.ncbi.nlm.nih.gov/31018108/

Typically #FSHD presents with face and periscapular weakness, but can demonstrate focal or asymmetric phenotypes

Great @MuscleAndNerve series here from my colleague Dr. Anhar Hassan outlining unusual presentations 8/8

onlinelibrary.wiley.com/doi/full/10.10…