Ross & Wilson Anatomy and Physiology in Health and Illness (196 page)

In most cases, the cause of OA is unknown (primary OA), but risk factors include excessive repetitive use of the affected joints, female gender, increasing age, obesity and heredity. Secondary OA occurs when the joint is already affected by disease or abnormality, e.g. trauma or gout. Osteoarthritis usually develops in late middle age and affects large weight-bearing joints, i.e. the hips, knees and joints of the cervical and lower lumbar spine. In many cases only one joint is involved.

Gout

This condition is more prevalent in males than females and there is a familial tendency. It is caused by the deposition of sodium urate crystals in joints and tendons, provoking an acute inflammatory response. Risk factors include obesity, heredity, hyperuricaemia and high alcohol intake.
Primary
gout, the commonest form, occurs almost always in men and is associated with reduced ability to excrete urate or increased urate production.
Secondary
gout occurs usually as a consequence of diuretic treatment or kidney failure, both of which reduce urate excretion.

In many cases only one joint is involved (monoarthritis) and it is typically red, hot and extremely painful. The sites most commonly affected are the metatarsophalangeal joint of the big toe and the ankle, knee, wrist and elbow joints. Episodes of arthritis lasting days or weeks are interspersed with periods of remission. After repeated acute attacks, permanent damage may occur with chronic deformity and loss of function of the affected joints. Gout is sometimes complicated by the development of renal calculi.

Connective tissue diseases

This group of disorders has common features. They:

•
affect many systems of the body, especially the joints, skin and subcutaneous tissues

•
tend to occur in early adult life

•
usually affect more females than males

•
are chronic conditions

•
are autoimmune diseases in which autoantibodies attack the individual’s tissues.

These disorders include the following.

•
Systemic lupus erythematosus
(SLE) – in this the affected joints are usually the hands, knees and ankles. A characteristic red ‘butterfly’ rash may occur on the face. Kidney involvement is common and can result in glomerulonephritis that may be complicated by chronic renal failure.

•
Systemic sclerosis
(
scleroderma
) – this is a group of disorders in which there is progressive thickening of connective tissue. There is increased production of collagen that affects many organs. In the skin there is dermal fibrosis and tightness that impairs the functioning of joints, especially of the hands. It also affects the walls of blood vessels, intestinal tract and other organs.

•
Rheumatoid arthritis
(
p. 422
).

•
Ankylosing spondylitis
(
p. 423
).

•
Reiter’s syndrome
(
p. 423
).

Carpal tunnel syndrome

This occurs when the median nerve is compressed in the wrist as it passes through the carpal tunnel (see
Fig. 16.50
). It is a common condition, especially in women, between the ages of 30 and 50 years. There is pain and numbness in the hand and wrist affecting the thumb, index and middle fingers, and half of the ring finger. Many cases are idiopathic or secondary to other conditions, e.g. rheumatoid arthritis, diabetes mellitus, acromegaly and hypothyroidism. Repetitive flexion and extension of the wrist joint also cause the condition, e.g. following prolonged keyboard use.

Diseases of muscle

Learning outcomes

After studying this section you should be able to:

list the causes of the diseases in this section

compare and contrast the characteristics of different types of muscular dystrophy.

Myasthenia gravis

See
page 376
.

Muscular dystrophies

In this group of inherited diseases there is progressive degeneration of groups of muscles. The main differences in the types are:

•
age of onset

•
rate of progression

•
groups of muscles involved.

Duchenne muscular dystrophy

Inheritance of this condition is sex linked, the affected gene being carried on the long X chromosome of female carriers. Their children may be affected by the condition if they are males (50% chance), or be carriers if they are females (50% chance) (see
Fig. 17.10, p. 434
).

Signs and symptoms may not appear until the child is about 5 years of age. Wasting and weakness begin in muscles of the lower limbs then spread to the upper limbs, progressing rapidly without remission. Death usually occurs in adolescence, often from respiratory failure, cardiac arrhythmias or cardiomyopathy.

Facioscapulohumeral dystrophy

This disease affects both sexes. It usually begins in adolescence and the younger the age of onset the more rapidly it progresses. Muscles of the face and shoulders are affected first. This is a chronic condition that usually progresses slowly and may not cause complete disability. Life expectancy is normal.

Myotonic dystrophy

This disease usually begins in adult life and affects both genders. Muscles contract and relax slowly, often seen as difficulty in releasing an object held in the hand. Muscles of the tongue and the face are first affected, then muscles of the limbs. Systemic conditions associated with myotonic dystrophy include:

•
cataracts (
pp. 204–205
)

•
atrophy of the gonads

•
cardiomyopathy

•
glucose intolerance.

The disease progresses without remission and with increasing disability. Death usually occurs in middle age from respiratory or cardiac failure.

Crush syndrome

Sustained pressure, on the trunk or a limb, causes ischaemia resulting in massive muscle necrosis. When pressure is relieved and circulation restored, myoglobin and other necrotic products are released from damaged muscle and enter the blood. This material is highly toxic to the kidneys and acute renal failure may develop. A common complication is infection, especially by anaerobic microbes, e.g.
Clostridium perfringens
, causing
gas gangrene
.

Rotator cuff injury

The rotator cuff muscles (
p. 404
) stabilise and strengthen the shoulder joint. Injury here is common, leading to pain and restricted mobility of the shoulder. Healing can take months or even years.

For a range of self-assessment exercises on the topics in this chapter, visit
www.rossandwilson.com
.

CHAPTER 17