Trunkal tremor: orthostatic or essential?

A sixty two year old man who presented with tremors of trunk and lower limbs, appearing only on standing, is reported. The tremor frequency was 14-16 Hz and there was co-contraction of antagonistic muscles. No therapeutic benefit was noted with propranolol, primidone and diazepam. The possible pathogenesis of this rare orthostatic trunkal tremor and its relationship with essential tremor are discussed.