The floppy infant

Question 1

Causes of Hypotonia

Answer 1

(I). Paralytic (From spinal cord to muscle)
1. Spinal cord lesion (Trauma, Poliomyelitis, SMA)
2. Peripheral nerve diseases
• Infection - Diphtheria
• Neuritis- GBS, CMT
• Drugs- Nitrofurantoin, Vincristine, Isoniazid
• Deficiency state - Thiamine, B12
• Heavy metal poisoning - Lead
• DM
• Riley Day Syndrome
• Hereditary

3. Neuromuscular junction disease
   • MG
   • Botulism

4. Myopathy
    • Congenital Myopathy
    • DMD
    • Polymyositis  
    • Metabolic disease - Cushings, Electrolyte disturbance, Hypothyroidsm, Pompe's disease

(II) Non- Paralytic

1. Normal CNS
    • Preterm
    • Major illness
    • Malnutrition
    • Metabolic - Scurvy, Rickets, Hypercalcaemia, Hypokalaemia, Hypothyroidism, RTA
    • Ligament laxity

2. Abnormal CNS
    • MR
    • CP
    • Birth asphyxia
    • Syndromes - Down's; Prada Wili, Lowe and Riley Day syndrome
    •  Storage disease
    • Aminoaciduria

3. Benign Congenital Hypotonia• Beware of early phase of paralytic disease which results in hypotonia eg. Early SMA, Early Myopathy

Question 2

Basic Investigations for Hypotonia

Answer 2

• Urinalysis
• Bloods x CBC, LRFTs, Ca, PO4, T4, TSH and CPK
• Imaging - SXR, CAT scan brain
• NCV & EMG
• Muscle Bx

Question 3

Familial Dysautonomia (Riley Day Syndrome)

Answer 3

• AD
• Common in Jews
• Features: FTT, Recurrent infections, Autonomic pain and temperature indifference, Peripheral neuropathy, Lack of tears, Corneal anaesthesia

Ix:
• Histamine test - normally causes pain and erythema followed by central wheal and surrounding flare
• Patient: Decrease pain response and no inflammation

Methacholine (5%)
• Instilled into corneal sac -> miosis within 10 min (A test of denervation hypersensitivity)
• Urine with increased HVA and decreased VMA level

Question 4

Tone assessment:

Answer 4

1. Hypertonous
   • Pyramidal tract: Resistance is speed sensitive (Claspknife rigidity)

• Extra pyramidal - 2 types of rigidity:

a. Cogwheel
b. Leadpipe

Hypotonous
Signs:
•  Frog like posture
•  Paucity of movement
•  Muscle bulk flabby
•  Increase range of movement
•  Decrease resistance to passive movement
•  'Slip through armpits' / LL sags
•  Delay gross motor development / Head lag / Round back/ Can't sit

Other features to look for:
• look for dimorphism eg. Prada Willi
• If no involvement of the face —> SMA
• Look at mother and shake her hands —> Myotonica Dystrophica
• Palpate Abdomen and look for Liver - Pompe’s / Type III Glycogen Storage disease