Approach to hand small muscles wasting

Question 1

Finger flexors and extensors

Answer 1

Flexors
MCP: lumbricals, interossei
PIP: FDS
DIP: FDP

Extensors
MCP: extensor digitorum
PIP: lumbricals, interossei
DIP: lumbricals, interossei

Question 2

Inspection of the hands

Answer 2

1. Unilateral or bilateral wasting?
2. Symmetrical or preferential/asymmetrical?
   - Ulnar neuropathy: intrinsic muscles (finger abduction/adduction, thumb adduction), 4th/5th finger DIP flexion and wrist flexion/ulnar deviation
   - Median neuropathy: thenar muscles (thumb opposition/abduction), weak pinch, forearm pronation, wrist flexion/radial deviation, flexion of thumb/index/middle fingers.
   - Watchout for concomitant median and ulnar neuropathy
3. Is there clawed hand? Is it due to ulnar neuropathy or imbalanced muscle strength?
4. Is there sensory loss?
5. Other features
   - General: neurofibromatosis, RA, cervical collar
   - Face: tongue fasciculation, myotonic facies
   - Eyes: Horner’s, ptosis, INO
   - Hands: clubbing, myotonia
   - Feet: pes cavus, FA, old polio
   - Legs: inverted champagn bottle
   - Gait: spastic paraparesis

Question 3

Thumb abduction
- Muscle
- Nerve
- Roots

Answer 3

Muscle: abductor pollicis brevis
Nerve: median nerve
Roots: C8, T1

Question 4

Thumb opposition
- Muscle
- Nerve
- Roots

Answer 4

Muscle: opponens policis
Nerve: median nerve
Roots: C8, T1

Question 5

Finger abduction
- Muscle
- Nerve
- Roots

Answer 5

Muscle: dorsal interossei (D-AB)
Nerve: Ulnar nerve
Roots: C8, T1

Question 6

Finger adduction
- Muscle
- Nerve
- Roots

Answer 6

Muscle: palmar interossei (P-AD)
Nerve: ulnar nerve
Roots: C8, T1

Question 7

Little finger abduction
- Muscle
- Nerve
- Roots

Answer 7

Muscle: abductor digiti minini
Nerve: ulnar nerve
Roots: C8, T1

Question 8

Split hand syndrome occurs in motor neuron disease where there is imbalance between medial (more denervated) than the lateral muscles
- Thenar more denervated than hypothenar
- First dorsal interosseous more denervated