Muscle diseases

Question 1

How do muscle diseases present?

Answer 1

Muscle pain
Muscle weakness/ tiredness
Stiffness
Abnormal blood tests

Question 2

Myopathy

Answer 2

disease of the muscle

Question 3

Polymyositis

Answer 3

Idiopathic inflammatory myopathy that causes symmetrical, proximal muscle weakness

Question 4

Histology of polymyositis (and dermatomyositis)

Answer 4

Muscle fibre necrosis, degeneration, regeneration and an inflammatory cell infiltrate.

Question 5

Presentation of polymyositis

Answer 5

Proximal (usually symmetrical) muscle weakness in the limbs (e.g. upper arms, upper legs).
It is insidious in onset (presents over several months).
Often patient presents with specific problems such as difficulty brushing hair etc.

Question 6

Pathogenesis of polymyositis and dermatomyositis

Answer 6

T-cell–mediated cytotoxic process directed against unidentified muscle antigens. CD8 T cells, along with macrophages, initially surround healthy nonnecrotic muscle fibers and eventually invade and destroy them.

An autoimmune response to nuclear and cytoplasmic autoantigens is detected in about 60-80% of patients with polymyositis and dermatomyositis. Some serum autoantibodies are shared with other autoimmune diseases (ANA, anti-RNP antibody), and some are unique to myositis (anti-Jo-1, anti-SRP antibodies).

Question 7

Systemic diseases that accompany polymyositis and dermatomyositis

Answer 7

Can be accompanied by dysphagia- secondary too oropharyngeal and esophageal involvement. This is a poor prognostic sign
Interstitial lung diseases.

Question 8

Investigations into polymyositis and dermatomyositis

Answer 8

Inflammatory markers are often raised.
Serum creatine kinase (CK) level is usually raised, often more than 10 times the normal level.
Autoantibodies include ANA, anti-Jo-1 and anti-SRP.

MRI- used to assess extent of muscle involvement
Electromyographic (EMG) findings are abnormal in almost all patients
MUSCLE BIOPSY is crucial in helping to diagnose polymyositis and in excluding other rare muscle diseases. Muscle biopsy shows muscle fibres in varying stages of inflammation, necrosis, and regeneration

Question 9

Treatment of polymyositis and dermatomyositis

Answer 9

Prednisolone (initially around 40mg) combined with disease modifying drugs such as methotrexate or azathioprine

Question 10

Dermatomyositis

Answer 10

Idiopathic inflammatory condition.

Question 11

Clinical features of dermatomyositis

Answer 11

Muscle pain
Proximal muscle weakness
Worsens over months
Gottrons papules- scaly red patches over the knuckles, knees and elbows.
Heliotrope rash- purply pink discolouration around the eyes
Shawl sign- red rash that comes down in a v shape at the front of the chest

Question 12

Which disease, polymyositis or dermatomyositis, has a higher malignant potential? And where do they commonly metastasise too?

Answer 12

dermatomyositis.

Ovarian, breast, stomach, lung, bladder and colon cancer.

Question 13

Presentation of dermatomyositis

Answer 13

Tired muscles, functional difficulty, muscle pain
Drugs- statins and steroids.
Other medical conditions- e.g. DM or thyroid disease.
Family history
Social- alcohol and ellicit drug use
Other symptoms- weight loss, cough, breathlessness, Raynauds.

Question 14

On examination of polymyositis and dermatomyositis, which tests would you perform?

Answer 14

Confrontational testing- directly pushing against the muscle to see if it is strong.
Isotonic testing- 30 second sit to stand test.

Question 15

Inclusion body myositis

Answer 15

Often misdiagnosed as polymyositis. Patient is often older (>50 years), and presents as distal muscle weakness.
Wrist and flexor muscles in upper limb, anterior tibial muscles and quadriceps in lower limbs.

Question 16

On biopsy- what does inclusion body myositis show?

Answer 16

Inclusion bodies.

Question 17

Polymyalgia rheumatica

Answer 17

Relatively common chronic inflammatory condition. Almost always in elderly (>50). Associated with temporal arteritis/giant cell arteritis.

Question 18

How does polymyalgia rheumatica present?

Answer 18

Proximal myalgia in the hip and shoulder girdles- symptoms occur over a few weeks. Presents as aching shoulders and morning stiffness.
After moving around for a bit they tend to get better, then sore again before going to bed or at periods of rest.
Usually symmetrical
Muscle strength is normal

Question 19

Giant cell arteritis/ temporal arteritis

Answer 19

Vasculitis of the temporal artery. Granulomatous deposit in the artery.

Question 20

Features of giant cell arteritis

Answer 20

Headache
Jaw claudication
Scalp tenderness
Tender, enlarged, non-pulsatile temporal arteries. 
Visual loss

Question 21

Treatment of polymyalgia rheumatica

Answer 21

Rapid and dramatic response to low dose steroids.
If the patient has temporal arteritis- higher dose steroid required.
Gradual reduction in steroid dose for around 18 months to 2 years.

Question 22

Diagnosis of polymyalgia rheumatica

Answer 22

Raised CRP and PV/ESR are almost always the case in polymyalgia rheumatica.
Temporal artery biopsy should be used for GCA

Question 23

Fibromyalgia

Answer 23

Common cause of MSK pain- not associated with inflammation. It is an unexplained condition that affects anyone (however is commonest in young and middle aged women).

Question 24

Pathogenesis of fibromyalgia

Answer 24

Disorder of central pain processing or a syndrome of central sensitivity. Patients tend to have a lower threshold of pain and of other stimuli, such as heat, noise, and strong odours

Question 25

Presentation of fibromyalgia

Answer 25

Persistent (>3 months) widespread pain. Pain can be around the neck and lower back- but patients often describe it as ‘hurting everywhere’.
Fatigue- disrupted sleep
Cognitive difficulties- find it difficult to concentrate.
Multiple unexplained conditions such as anxiety and depression.
Symptoms often become worse with exertion and stress.

Question 26

Clinical findings of fibromyalgia

Answer 26

Excessive tenderness on palpation of soft tissues
11/18 tender points
No other abnormality of musculoskeletal system

Question 27

Diagnosis of fibromyalgia

Answer 27

No diagnostic tests
Inflammatory markers normal
Absence of other explanation of symptoms

Question 28

Treatment of fibromyalgia

Answer 28

Patient education
Graded exercise programme
CBT
Antidepressants may help with sleep pattern e.g. tricyclics. Analgesia
Gabapentin