A 35-year-old female presents with a 2-week history of progressive weakness and wasting of the small muscles of her left hand. On examination, she has a claw hand deformity (hyperextension at the metacarpophalangeal joints and flexion at the interphalangeal joints), weakness of finger abduction and adduction, and sensory loss over the medial one-and-a-half fingers and medial aspect of the palm. She reports a history of a pancoast tumour invading the lower trunk of the brachial plexus. Which nerve roots are involved in this injury?

Explanation

## Klumpke's Palsy: Lower Trunk Brachial Plexus Injury The patient presents with a classic **Klumpke's palsy** (lower trunk injury), characterized by distal hand weakness and a claw hand deformity. ### Motor Deficits - **Claw hand deformity** → Paralysis of intrinsic hand muscles (interossei and lumbricals) - **Weakness of finger abduction and adduction** → Interossei paralysis (ulnar nerve, C8–T1) - **Weakness of thumb opposition and flexion** → Thenar and hypothenar muscles (ulnar and median nerves, C8–T1) ### Sensory Deficits - **Medial one-and-a-half fingers** (little finger + medial half of ring finger) → Ulnar nerve (C8–T1) - **Medial aspect of palm** → Ulnar nerve cutaneous distribution (C8–T1) ### Anatomical Basis | Nerve Root | Motor Supply | Sensory Supply | Clinical Correlation | |---|---|---|---| | **C8** | Intrinsic hand muscles, finger flexors | Medial forearm, medial 1.5 fingers | Claw hand | | **T1** | Intrinsic hand muscles, hand abductors | Medial hand, axilla | Horner's syndrome (if sympathetic fibers involved) | | C5–C6 | Shoulder/arm muscles | Lateral arm/forearm | NOT affected in Klumpke's | | C7 | Wrist/finger extensors | Dorsal middle finger | NOT affected in Klumpke's | **Key Point:** Klumpke's palsy results from injury to the **lower trunk** of the brachial plexus, formed by **C8 and T1 nerve roots** only. Common causes include: - Pancoast tumour (as in this case) - Cervical rib compression - Traction injuries (hyperabduction of arm) - Birth trauma (less common than Erb's) **High-Yield:** The **claw hand** is the hallmark sign of C8–T1 involvement: - Unopposed action of long finger extensors (supplied by C7) causes hyperextension at MCP joints - Paralyzed intrinsic muscles cannot extend IP joints, causing flexion - Result: "Claw" appearance **Mnemonic: CLAW = C8–T1 Lower trunk Affects Wrist-intrinsic muscles** **Clinical Pearl:** If Horner's syndrome (miosis, ptosis, anhidrosis) is present alongside Klumpke's palsy, it indicates involvement of T1 sympathetic fibres, strongly suggesting a Pancoast tumour or cervical rib compressing the lower trunk at its origin from the spinal cord.