Lower motor neurone signs

Question 1

LMN signs on examination

Answer 1

Wasting
Fasciculation
Hypotonia
Hyporeflexia

Question 2

Causes of bilateral, symmetrical, and distal LMN signs

Answer 2

(“Motor peripheral polyneuropathy”, or + sensory disturbance = “mixed peripheral polyneuropathy”)
DDx:
Hereditary Motor and Sensory Neuropathy (HMSN)
Paraneoplastic e.g. LEMS
Lead poisoning
Acute: GBS, Botulinum

Question 3

Causes of bilateral, symmetrical and proximal LMN signs

Answer 3

“Proximal myopathy”
Inherited: muscular dystrophy
Inflammation: polymyositis, dermatomyositis
Endocrine: Cushing’s syndrome, acromegaly, thyrotoxicosis, osteomalacia, diabetic amyotrophy
Drugs: alcohol, statins, steroids
Malignancy: paraneoplastic

Question 4

Causes of unilateral LMN signs

Answer 4

Isolated to single limb + no sensory signs: Old polio

Localised to group of muscles with same supply: segmental - nerve roots, plexus, peripheral - mononeuropathy

Question 5

Causes of hand wasting

Answer 5

Anterior horn: syringomyelia, MND, polio
Roots (C8 T1): spondylosis
Brachial plexus: compression from cervical rib, avulsion (Klumpke’s palsy)
Neuropathy: generalised (HMSN), mononeuritis multiplex (DM), compressive mononeuropathy.
Muscular: disuse - RhA, distal myopathy - myotonic dystrophy.

Question 6

Investigations for proximal myopathy

Answer 6

Bloods: 
DM - glucose, HbA1c
Muscle damage - CK, ESR, AST, LDH
Endocrine - TSH, Ca, 9am cortisol, IGF-1
Antibodies: anti-Jo-1
CXR: paraneoplastic
EMG
Genetic analysis
Muscle biopsy

Question 7

Investigations for mononeuropathy

Answer 7

Bloods:
DM - glucose, HbA1c
B12, folate
Vasculitis - ESR, ANA, ANCA
EMG & nerve conduction

Question 8

Investigations for radiculopathy/plexopathy

Answer 8

MRI