Which movement pattern is described by arms stiffly extended, adducted, internally rotated, and legs stiffly extended with plantar flexion?

• A. Decorticate rigidity
• B. Decerebrate rigidity
• C. Chorea
• D. Tics

Answer: (B)

This question tests recognition of brainstem-origin posturing. In decerebrate rigidity, the body adopts a characteristic extension pattern driven by loss of inhibitory control from higher brain regions over brainstem pathways. The arms become stiffly extended, held close to the body, with adduction and internal rotation. The legs also extend, and the feet point downward into plantar flexion. This pattern reflects a lesion at or below the midbrain/upper pons, where descending pathways that normally modulate extensor tone are disrupted, so extensor (rather than flexor) circuits dominate.

For context, decorticate rigidity shows the arms flexed at the elbows with adduction and internal rotation, while the legs may extend—this difference in arm posture helps distinguish the two. Chorea and tics are involuntary, not sustained postures, so they do not describe this rigid extension pattern.