Which conditions are characterized by dissociated sensory loss, where the patient can feel the lightest touch but cannot distinguish one end of a pin from the other?

A sign of particular importance is dissociated sensory loss where the patient can feel the lightest touch in the affected area, but is unable to distinguish one end of a pin from the other. Selective involvement of the pain pathways is a feature of syringomyelia, hemi-cord lesions (Brown–Séquard syndrome) and the lateral medullary syndrome (Wallenberg syndrome). Syringomyelia is associated with selective involvement of pain pathways. Patients experience dissociated sensory loss, where they can perceive light touch but struggle to differentiate between the ends of a pin. Other conditions, such as hemi-cord lesions (Brown–Séquard syndrome) and lateral medullary syndrome, may also exhibit similar features. Keep this in mind during your clinical assessments!