**7. Differential diagnosis**

Cellulitis is perhaps the most common finding in women that can provoke some difficulties in the clinical diagnosis of LS. To differentiate them clinically, it is helpful to stretch the skin with the fingers, and try to detect depression, which is not a feature of cellulitis [6]. Another probably common form of localized lipoatrophia is

#### *Rare Diseases – Recent Advances*

#### **Figure 3.**

*Ultrasound of semicircular lipodystrophy in both thighs. Slight atrophy and heterogeneous echostructure of the subcutaneous cellular tissue in both thighs. The subcutaneous echostructure alteration predominates in the superficial segment (top image; right side). The image at the bottom shows the measurement of the subcutaneous thickness of the affected area (2.09 cm) compared to the adjacent segment that is toward the head (1.79 cm). The arrows point out the segments of subcutaneous atrophy (Image courtesy of Dr. Ximena Wortsman).*

the so-called "leg crossers' dimple," which affects patients with a long history of leg crossing. The lesion consists of an indentation on the leg, which correlates with the site where the patella rests over the other knee. It is more common in females and it is probably caused by repeated local pressure that may destroy adipocytes. Some cases may present with lichenification of the zone, perhaps related with recurrent rubbing in patients that frequently jitter while crossing legs ("agitated leg crossers") [77].

In infancy, there are several acquired conditions that clinically may present with linear circumferential or partially circumferential lesions associated with trauma, or because of wearing elastic bands of socks or pantlegs [78]. They produce inflammation in the fat and dermis and hyperpigmentation, plus raised or atrophic bands. At this age, other infantile curvilinear lesions should be considered, such as child abuse,

#### *Lipoatrophia Semicircularis DOI: http://dx.doi.org/10.5772/intechopen.105920*

amniotic band syndrome, linear and whorled hyperpigmentation, and incontinentia pigmenti. All these clinical pictures differ from LS in clinical history, histopathological findings, and presence of hyperpigmentation.

Partially localized lipoatrophy has been described in connection with subcutaneous, intramuscular, or intra-articular injections. Treatment with methotrexate [38], corticosteroids, insulin (prior to the development of purified insulin in the 1970's) [79], and benzathine penicillin [39, 80] have been associated with lipoatrophy. Its appearance is common in children, and varies from simple pitting areas of the skin to large and disfiguring athrophies. The trauma of injection rather than the medication injected is mainly the cause of the panniculitis. The lesions appear only on injection sites, which rarely adopt a band distribution, and a loss of subcutaneous fat is present. Depressed cutaneous lesions resulting from insulin injection spontaneously disappear within 1–3 years. Other agents implicated in localized lipoatrophy are vasopressin, human growth hormone, iron dextran, and diphtheria–pertussis– tetanus (DPT) vaccine.

In patients with autoimmune disorders, localized subcutaneous atrophy of the extremities can be seen. Connective tissue diseases represent a predisposing factor for the development of bands or rounded atrophic lesions. LS should be differentiated from other atrophies in patients with lupus erythematosus, morphea, panniculitis, and lupus panniculitis, which may affect children and adults. In morphea the plaques are pearly and whitish, the skin is indurated and sometimes an erythematous halo is visible [81]; this is never found in LS. Some cases adopt a linear distribution, characterized by single and unilateral streaks of cutaneous induration that may involve deeper structures like dermis, subcutaneous tissue, and occasionally muscle and underlying bone. Lupus lesions tend to be localized in arms, face, and buttocks, mainly as deep nodules of a long evolution, covered with normal skin or lesions that evolve to atrophic scars during regression [31]. Lupus panniculitis lesions are usually located in the upper body and present with a scarring appearance [67]. Factitious panniculitis is clinically visible as recurrent episodes of nodules mainly located in the extremities, associated with other factitious lesions; histopathological findings show granulomatous panniculitis.

Underlying autoimmune diseases -if present- are responsible for a protracted course. Localized lipoatrophy associated with recessive dystrophic epidermolysis bullosa has also been reported [82].

Other causes of localized lipoatrophy include treatment with oral retroviral drugs in HIV/AIDS patients and association with lyme disease (*Borrelia burgdorferi* infection).

Two other clinical pictures of localized band lipoatrophy that may resemble LS have been described: annular lipoatrophy and annular lipoatrophy of the ankles.

The first entity was described by Ferreira–Marques in 1953 [83], affecting the forearm of a woman, with further two other cases reported by Bruinsma in 1967 [84]. In annular lipoatrophy, a circular and depressed pseudosclerodermic band of 1 cm wide and 0.5–2 cm deep around the arm is described. It appears mainly between 40 and 70 years old, it is monolateral, with a maximum width of 1 cm, and might be associated with pigmentation. The band is preceded by swelling and tenderness of the entire limb and fever in the original case. Distal swelling of the arm plus neuralgia and arthralgia pain associated with muscle weakness are additional features. Bruinsma's first case was also associated with myopathy. The band was persistent for more than 20 years. Histopathological studies showed loss of the subcutaneous fat replaced by strands of connective tissues and polyarthritis with venous thrombi.

Annular atrophy of the ankles was reported initially in 1970 and later in 1975 [85, 86]. The lesions appear in the ankles but can also affect feet and legs; most cases have been reported between 6 and 35 years old, with bilateral distribution and wider than LS and lipoatrophia annularis, ranging from 9 to 11 cm. The skin appears normal, although edema before atrophy was described in one case. No changes in color or consistency occur and local symptoms or muscle involvement are absent. Histopathological study shows an early inflammatory stage, with mononuclear infiltration in the subcutis, neoformation of blood vessels, and replacement of adipose lobules with connective tissue.
