Proximal myopathy

The clinical diagnosis of proximal myopathy is usually straightforward. Proximal muscle wasting and weakness is easily demonstratable.

Tips:
**The weakness is bilateral and usually symmetrical.
**The sensory is always INTACT!

The causes that you need to consider are:
1. Muscular dystrophy
**Duchenne/ Becker muscular dystrophy (look for pseudohypertrophy of calf muscle
** Fascioscapulohumeral dystrophy (look for facial muscle weakness)
**Limb girdle muscular dystrophy

2. Inflammatory muscle disease
** Polymyositis (muscle may be tender)
** Dermatomyositis (Facial heliotrope rash and Gottron's sign)

3. Endocrinopathy
** Cushing's syndrome
** Thyrotoxicosis
** Acromegaly
**ALL will have obvious external features

4. Metabolic myopathies
** Hypo/hyperkalemia, Hypo/hypercalcemia

The above patient with proximal myopathy also has features of Cushing's syndrome. Remember that Cushing's syndrome can cause proximal myopathy but also do not forget that steroid use for polymyositis/dermatomyositis can also cause Cushing's syndrome.

How do you differentiate polymyositis, dermatomyositis and inclusion body myositis ?

Polymyositis Dermatomyositis Inclusion body myositis

Sex F>M F>M M>F

Age Adult Childhood & Adult Elderly > 50 years old

Rash Yes No No

Distribution of weakness Prox > Distal Prox > Distal Prox = Distal,

predilection for

finger/wrist flexion,

knee extensors

CK incr (up to 50x) N or incr (up to 50x) N or mildly incr (<10

x N)

Muscle biopsy amyloid deposits

Response to

immunosupressive Yes Yes No or minimal

EMG myopathic myopathic myopathic/neuropathic