**Question:** In TB spine the first symptom is:

A. Back pain
B. Weakness in lower limbs
C. Radiating pain to lower limbs
D. Cervical spine involvement

**Core Concept:**

Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis. It primarily affects the lungs (pulmonary TB), but can also involve other organs, including the spine. TB spine, also known as vertebral TB, presents with a variety of symptoms depending on the spinal segment involved.

**Why the Correct Answer is Right:**

The correct answer, **A. Back pain**, is the most common initial symptom of TB spine. The bacterium can invade the vertebrae and cause inflammation and destruction of the bone, leading to spinal instability and pain. Since the spine is involved, the pain typically radiates along the dermatomes (spreads along sensory nerves) and may be exacerbated by movements.

**Why Each Wrong Option is Incorrect:**

**B. Weakness in lower limbs (Option B)** is incorrect because TB spine usually affects the thoracic or lumbar spine, which is less likely to cause lower limb weakness compared to cervical spine TB. Weakness is more commonly seen with spinal cord compression or nerve root involvement in cervical spine TB.

**C. Radiating pain to lower limbs (Option C)** is partially correct but not the most common initial symptom. Pain radiating to lower limbs is usually present in cases of TB spine affecting the cervical spine, where the spinal cord is compressed. TB spine involving other regions (thoracic or lumbar) typically causes pain that is more localised.

**D. Cervical spine involvement (Option D)** is incorrect as TB spine can involve any segment of the spine, not restricted to the cervical spine. The correct answer, A (back pain), is more general and applies to all regions affected by TB spine.

**Clinical Pearl:**

In suspected cases of TB spine, a thorough clinical examination focusing on back pain distribution and associated symptoms (such as weakness, numbness, or bowel/bladder dysfunction) is crucial. Diagnostic investigations like imaging studies (X-rays, CT scans, or MRI) are essential to confirm the diagnosis and determine the spinal segment involved. Early recognition and treatment of TB spine can prevent further complications like spinal cord compression and neurological deficits.