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DISORDERS OF THE FAT AND SUBCUTANEOUS TISSUES

This section will discuss three groups of disorders, namely:

Figure 22.40 Linear focal elastosis. These lesions occur on the mid- and lower back. They resemble striae due to vertical growth in adolescents, but occur in elderly men, and may represent elastotic degeneration or regeneration of striae. They are yellowish, raised, and contain fragmented elastic tissue on pathologic examination.

Figure 22.41 Acrokeratoelastoidosis is an uncommon disorder, which manifests as translucent or keratotic papules along the border of the palms. It is morphologically similar to focal acral hyperkeratosis, but is more common in dark-skinned patients and often an older age group. Biopsy to demonstrate elastic tissue abnormalities is required to distinguish between these disorders.

Figure 22.42 Older insulins often caused localized lipoatrophy at frequent injection sites. In some instances, as shown here, both lipoatrophy and lipohypertrophy have occurred.

Figure 22.43 Intralesional steroid injection for tendinitis at the elbow, causing some atrophy. Hypopigmentation is a commonly associated feature, which may also extend proximally along the line of lymphatic vessels but usually resolves.

Figure 22.44 Atrophy at depot steroid injection sites. This degree of deep atrophy is unusual, and it is uncertain why some individuals get such marked atrophy, but the changes are usually permanent.

Lipoatrophy and lipodystrophy

Lipoatrophy

Lipoatrophy may be localized, partial (upper trunk), or total; it may occur in isolation or associated with atrophy of other deeper structures (such as panatrophy).

    Localized areas of lipoatrophy may occur in the following situations.

Lipodystrophy

The most frequent of these uncommon disorders is partial lipodystrophy . This is poorly understood but may have an autoimmune basis. It may be familial. Most patients have a gradual loss of fat from the face and upper trunk, causing a cadaverous facies and easily visible musculature (Fig.22.47); in women, in whom it is most frequent, it may be mistaken for a hyperandrogenic state. In some cases, there is a compensatory lipohypertrophy of the lower limbs.

    The importance of this disorder is an association with mesangiocapillary glomerulonephritis, which occurs in the majority of affected individuals and which may be accompanied by complement C3 deficiency and diabetes. This may present during pregnancy or oral contraceptive use.

    Total lipoatrophy is a much less common, autosomal recessive disease in which hyperlipidemia and insulin-resistant diabetes occur; hypertrichosis and complete loss of fat occur in infancy, diabetes occurring later. An acquired form, sometimes triggered by a febrile illness, also occurs.

Figure 22.45 Spontaneous lipoatrophy on the flank, a pattern known as lipoatrophia centrifugalis.

Figure 22.46 Semicircular lipoatrophy (lipoatrophia semicircularis) at the typical anterolateral thigh site in a woman. Although originally felt to be idiopathic, larger series of cases suggest that pressure related to hard seats or from leaning against a desk or bench may be the cause of this disorder. (Courtesy of Dr. I. Coulson.)

Figure 22.47 (a) Partial lipodystrophy affecting the face, producing a gaunt, cadaverous appearance due to easily visible underlying bony structures. (b) Partial lipodystrophy in a man with associated renal disease. The deltoid muscle is easily visible due to loss of the overlying fat. (Panel a courtesy of Theodore Sebastian, M.D.)

Lipohypertrophy and lipedema

Lipohypertrophy

Lipohypertrophy may occur as a localized phenomenon, multiple discrete lesions, or more diffusely. The most frequent type of localized lipohypertrophy is a lipoma, a benign tumor of adipose tissue. These may be solitary or multiple (Fig. 22.48), the multiple lesions often being familial. Multiple discrete or more extensive areas of painful adiposity occur in Dercum disease (adiposis dolorosa), and isolated angiolipomas are also painful. Localized lipohypertrophy was also related to insulin injections (see Fig. 22.42), but it is now rare since the introduction of synthetic human insulins.

    More extensive areas of lipohypertrophy occur in multiple symmetric lipomatosis (Madelung disease, Fig.22.49). Lipohypertrophy may occur as a compensatory feature in partial lipodystrophy (discussed earlier), and centripetal adiposity occurs in Cushing syndrome (Ch.12). In cellulite (Fig.22.50), the dimpled appearance is due to fibrous tethering within the fat, rather than simply due to increased fatty tissue. A lipodystrophic disorder with central lipohypertrophy (buffalo hump, increased abdominal fat, and breast hypertrophy) has been reported in patients with AIDS, the majority of cases being related to treatment with protease inhibitors.

Lipedema

Lipedema is a condition in which there is soft fatty swelling of the lower leg. It can be distinguished from simple edema or lymphedema by the fact that it is sharply limited at the ankle, the foot being unaffected. It also fails to respond to diuretics or compression.

Panniculitis

Etiology and pathogenesis

Panniculitis is an inflammation of fat. Methods of classification may be based on the causative mechanisms, the type of cellular infiltrate, the structures that are affected within the fat, and the presence of vasculitis. The most helpful approach is to divide panniculitis on histologic grounds according to the part of its structure that is predominantly affected by the inflammatory process. Fat has two components, namely lobules made up of fat cells and septa between these (in which the vascular supply traverses the fat). Assessment of the pathologic ‘center of gravity' of the inflammation, i.e. mainly septal or mainly lobular, can be used to create a likely list of causative disorders; these can then be subdivided according to the presence or absence of vasculitis, and by the type of inflammatory infiltrate that is present. For example, primarily vasculitic causes of panniculitis, such as polyarteritis nodosa, cause a predominantly septal pattern of inflammation, whereas agents that directly damage the fatty tissue (such as cold injury or pancreatic lipase) cause a lobular panniculitis.

Figure 22.48 Lipomas on the arm. Multiple lipomas of this type are often familial but are often asymptomatic.

Figure 22.49 Madelung disease (multiple symmetric lipomatosis). This occurs mainly around the neck and shoulders in men.

Figure 22.50 Cellulite is a cosmetic change in fatty tissue that is usually most apparent in women on buttocks and thighs, due to increased fatty tissue with fibrous tethering that causes a dimpled appearance.

Figure 22.51 Panniculitis at a typical lower leg site: no specific diagnosis was made, possibly because (as suggested by the tethered appearance) the lesions were old. (Courtesy of Dr. L. Barco.)

   Some causes of panniculitis, classified in this manner, are listed in Table 22.3. However, it must be acknowledged that there are often components of both lobular and septal inflammation present, especially in established lesions.

Clinical

Most panniculitis lesions present as one or several deeply situated tender nodules. Inflammation is prominent in some causes, such as erythema nodosum. Lesions are typically on the lower legs or over fatty areas in the most common variants (Fig. 22.51). A particular variant that can often be suspected clinically is lupus panniculitis (lupus erythematosus profundus, see Fig. 13.32); this typically affects the upper trunk or upper arms in young women, who usually have other features of lupus erythematosus. Panniculitis due to cold injury is also often clinically distinctive, occurring over lateral thighs or upper arms and with markedly cold lesions (Fig.22.52).

    Discharge of liquefied fat may occur from lesions of panniculitis. Calcification may occur in panniculitis due to renal disease (vessel wall calcification or interstitial calcification), injury with dystrophic calcification, pancreatic panniculitis, or autoimmune disease.

    The clinical features of panniculitis lesions themselves may be characteristic of a specific diagnosis in some cases, such as most examples of erythema nodosum or cold injury. However, most causes of panniculitis are diagnosed from associated clinical features, biopsy features, or other tests; note also that diagnosing an eruption as erythema nodosum does not identify the triggering cause.

Differential diagnosis

The differential diagnosis may vary according to the clinical pattern — site(s) affected, number of lesions, etc.—but may include the following.

The most important differential is usually between the different causes of panniculitis.

Treatment

The treatment of panniculitis depends on the cause; for example, lupus panniculitis is often responsive to oral antimalarials, and pancreatic panniculitis due to a carcinoma requires treatment of the tumor.

Figure 22.52 Cold-induced panniculitis. (a) Equestrian panniculitis. This variant of chilblains is a clinically characteristic but often misdiagnosed type of cold-induced panniculitis. It occurs on the lateral thighs, typically in young women, as red, tender, indurated confluent or annular plaques. They are dramatically cold to touch despite the burning pain sensation. It characteristically occurs in horse riders (hence the name) but many also occur in others who get cold, wet legs for prolonged periods. (b) A similar lesion, in this case affecting the fatty tissue of the arm. This is a less common site for cold panniculitis, presumably because the arms are usually better protected by clothing, and are able to be warmed by contact with the trunk.

Erythema nodosum

Etiology

Erythema nodosum (EN) is the commonest form of panniculitis and is therefore discussed specifically. It is a reaction pattern that occurs due to a variety of triggers (Table 22.4). Histologically, there is a septal panniculitis that is initially neutrophilic but later lymphocytic.

Clinical features

The lesions of EN are red, tender, deeply placed nodules (Fig.22.53) that become more bruise-like as they disappear over a few weeks. They usually occur on the shins, and are usually multiple and bilateral. Other sites, such as the thighs or arms, may also be affected, occasionally without lesions on the lower legs. There may be associated fever, malaise, arthralgia, sore throat, or cough, which are partly due to an acute-phase response but also relate to the underlying causes. Elevated plasma viscosity, erythrocyte sedimentation rate, leukocytosis, thrombocytosis, and elevated complement C3 and C4 levels may occur as part of the acute response. Investigations should be determined by the likely causes based on clinical history. Streptococcal infection is a common cause that may be identified in retrospect by a raised antistreptolysin O (ASO) titer. Chest radiography is important in patients without a clinically obvious trigger, as about a third of cases are due to acute sarcoidosis, which may be suspected by finding bilateral hilar lymphadenopathy.

    A less common type, known as chronic or migratory EN, occurs as a chronic disorder in middle-aged women.

Figure 22.53 Examples of erythema nodosum. (a–c) The legs are the most common site, and the lesions are typically painful.

Differential diagnosis

This is as for other forms of panniculitis, mainly skin infections or ecchymoses.

Treatment

Acute attacks are usually treated with rest, non-steroidal antiinflammatory drugs, and occasionally systemic steroids, depending on severity of symptoms and the nature of any associated disorder. For more chronic lesions, potassium iodide, colchicine, intralesional steroids, antimalarials, dapsone, and immunosuppressive agents may all have benefit.

White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.