I-Beam Sign in Progressive Supranuclear Palsy

Postural instability occurs in both progressive supranuclear palsy (PSP) and idiopathic Parkinson's disease (IPD).

Testing for postural instability using a pull test helps to differentiate IPD from PSP based on the presence of an I-beam sign in the latter.

Here, we demonstrate the I-beam sign in a 65-year-old lady who presented with initial marked postural instability.

In PSP, postural instability occurs early. Here, we found that in patients with PSP on the backward pull test, they fall without taking a single step, like a building falls without an I-beam. This sign is called I-beam sign. In patients with IPD, this sign is absent as they take one or a few steps before falling. Clinical examination showed mild restriction of upward gaze, and there was radiological evidence of midbrain atrophy. The present case was diagnosed as PSP with a postural instability variant.

The presence of the I-beam sign in patients with Parkinsonism suggests PSP.