Carpal tunnel syndrome (CTS) may be overlooked in the absence of typical sensory symptoms. Two patients with CTS lacked the attendant sensory symptoms but experienced difficulties performing a pinching action behind the back (manipulation of the buckle of a baby sling or the hook of a brassiere), a mode of pinching that required wrist flexion. The causative mechanism was probably exacerbation of a latent weakness of the intrinsic muscles of the thumb by wrist flexion, in which the strength of the extrinsic flexors of the thumb and index finger were decreased due to loosening of the tendons. Such symptoms, induced by a specific wrist position, may be help to diagnose a latent weakness in the intrinsic muscles of the thumb, present in patients with CTS.