DISORDERS OF COLLAGEN AND ELASTIC TISSUE:

Ehlers-Danlos syndrome (see also p. 602)
Ehlers-Danlos syndrome can be subdivided into at least 10 variants. They are all inherited disorders causing abnormalities in collagen of the skin, joints and blood vessels. Clinically this causes increased elasticity of the skin, hypermobile joints and fragile blood vessels causing easy bruising or in some cases internal haemorrhage. The skin is hyperextensible but recoils normally after stretching. It is easily injured and heals slowly with scarring like tissue paper. Pseudotumours may occur at the sites of scarring (such as elbows and knees) consisting mainly of fat, but calcification can occur.
Pseudoxanthoma elasticum
Pseudoxanthoma elasticum is a rare group of disorders characterized by abnormalities in collagen and elastic tissue affecting the skin, eye and blood vessels. The skin may be loose, lax and wrinkled. It can look yellowish and papular ('plucked chicken skin') and tends to lose its elastic recoil when stretched. Skin changes are best seen in the flexures especially the sides of the neck. Non-cutaneous features are not always present but they include recurrent gastrointestinal bleeding, early myocardial infarction, claudication and angioid streaks on the retina reflecting disruption of vascular elastic tissue.
Marfan's syndrome (see also p. 839)
Marfan's syndrome, an autosomal dominant disorder of connective tissue, is described on page 839. The syndrome is characterized by tall stature and long thin digits (arachnodactyly) (Fig. 13.98). The arm span can exceed the height of the patient and a high arched palate may be present. Lax ligaments result in frequent dislocation of joints. Inguinal and femoral hernias are common. Scoliosis and flat feet may be present. Pulmonary changes include emphysema, diaphragmatic hernia and spontaneous pneumothorax. Dislocation of the ocular lens is common. Skin changes are usually absent but striae may develop. Patients with homocystinuria (see p. 602), type III and VI Ehlers-Danlos syndrome (EDS) and 'marfanoid phenotype' have some similar features but often do not develop the life-threatening complications of Marfan's syndrome, so accurate diagnosis by an expert is essential.
Treatment
Patients should be reviewed by an ophthalmologist, an orthopaedic surgeon and a cardiologist to screen for and deal with the above complications. Genetic counselling should be offered to families.
Striae

Striae are visible linear scars due to dermal collagen damage and stretching. Histologically a thinned epidermis overlies parallel bundles of fine collagen. They occur commonly over the abdomen and breasts in pregnancy but also occur on the thighs and trunk in rapidly growing adolescents as well as in some obese individuals. They are also seen in Cushing's syndrome and corticosteroid therapy. Striae are initially reddish blue but fade to white atrophic marks. Puberty-related striae normally disappear completely.
Keloid scars
Keloid scars are characterized by smooth hard nodules (Fig. 23.36) due to excessive collagen production. They may occur spontaneously or follow skin trauma/surgery, and they are often itchy. They tend to affect young adults and are much commoner in black Africans. Sites of predilection include the shoulders, upper back and chest, ear lobes and the chin. Unlike hypertrophic scars (which fade within 12 months) keloids are persistent and may fade with time.
Treatment is with triamcinolone injection, compression with silica gels or surgery but the latter must be followed by steroid injection or superficial radiotherapy or it may make the problem worse.
FURTHER READING
Hu X et al. (2003) ABCC6/MRP6 mutations: further insight into the molecular pathology of pseudoxanthoma elasticum. European Journal of Human Genetics 11: 215-224.
Ohtani T et al. (2002) Pseudoxanthoma elasticum. Journal of Dermatology 29: 615-620.
Wordsworth P et al. (2001) The real connective tissue diseases. Clinical Medicine 1: 21-24.