**Question:** Trendelenberg sign is positive in paralysis of all except -

A. Lumbar sympathetic plexus
B. Cervical spinal cord
C. Brachial plexus
D. Lumbar sympathetic plexus

**Correct Answer:** **A. Lumbar Sympathetic Plexus**

**Core Concept:** Trendelenberg sign is a clinical examination maneuver used to assess for orthostatic hypotension and assess the integrity of the autonomic nervous system. It involves measuring the change in blood pressure and heart rate when an individual stands up from a recumbent position. A positive sign indicates a disturbance in the autonomic nervous system.

**Why the Correct Answer is Right:** The Trendelenberg sign is generally positive in conditions affecting the spinal cord or peripheral nerves. In the case of lumbar sympathetic plexus paralysis (option D), the autonomic dysfunction is primarily affecting the sympathetic fibers, leading to a positive sign. However, the lumbar sympathetic plexus is not the correct answer. The lumbar sympathetic plexus is responsible for supplying the lower extremities, while the Trendelenberg sign is specifically assessing the integrity of the sympathetic fibers in the autonomic nervous system.

**Why Each Wrong Option is Incorrect:**

**A. Lumbar Sympathetic Plexus:** As mentioned earlier, the lumbar sympathetic plexus is responsible for supplying the lower extremities and not the autonomic nervous system. Therefore, it is not the correct answer for a sign assessing sympathetic fibers.

**B. Cervical Spinal Cord:** The cervical spinal cord is responsible for controlling voluntary movements and sensory functions, not autonomic functions. Assessing the cervical spinal cord would not be relevant for evaluating the Trendelenberg sign.

**C. Brachial Plexus:** The brachial plexus is responsible for supplying the upper limb muscles and sensory functions. Assessing the brachial plexus is irrelevant to evaluating the Trendelenberg sign.

**Clinical Pearl:** The Trendelenberg sign is primarily assessed in conditions affecting the spinal cord (cervical region), brainstem (midbrain and pons), or peripheral nerves (radial and ulnar nerves). It is generally positive in conditions involving the upper motor neuron lesions, such as the cervical spinal cord or brainstem lesions. This test helps diagnose conditions like cerebral palsy, multiple sclerosis, and certain stroke syndromes. In summary, the correct answer is A, as it involves the cervical spinal cord, which is relevant to evaluate the Trendelenberg sign.