Which of these is a hallmark sign of Klumpke's paralysis?

Klumpke's paralysis, a type of brachial plexus injury, is characterized by damage to the lower trunk of the brachial plexus, often affecting the C8 and T1 nerve roots. A hallmark sign of this condition is the absence of grasp in the affected hand. This inability to grasp is due to the weakness or paralysis of the muscles that control hand function, particularly the intrinsic muscles of the hand that are responsible for gripping.

In Klumpke's paralysis, the affected limb may appear to hang by the side and lack muscle tone, making it difficult or impossible to perform gripping actions. This symptom is crucial for diagnosis and helps differentiate Klumpke's paralysis from other conditions that may also affect the arm but with different muscle function patterns.

The other potential signs, such as elbow flexion or shoulder rotation, are inconsistent with this type of paralysis. While some degree of mobility may still be present, the primary concern in Klumpke's is the specific dysfunction of the hand and grasping ability. The Moro reflex can also be asymmetric in various conditions, but it is not directly indicative of Klumpke's paralysis. Overall, the absence of grasp is a defining and significant sign for this particular diagnosis.