62.4 Mechanism of Action/Histology

PLLA differs from other fillers in that it is dependent on the host response to accomplish filling. Clinically, this is represented by an initial volume effect, due to the volume of hydrogel (diluent water plus PLLA microparticles) injected. This effect lasts up to 1 week. The secondary, long lasting clinical effect is believed to involve collagen synthesis, which by definition is a delayed mechanism of action. PLLA is one of the few soft tissue fillers which can be termed a true biocatalyst or biostimulant [35–37]. Since the host immune response is involved in fibroblast behavior to some degree, and fibroblasts are responsible for collagen synthesis, potential differences to treatment with PLLA in patients with an intact immune system have been proposed as possible. In terms of response to treatment, in the authors over 8 years of experience with both cosmetic and HIV patients, this has not been the case. Cosmetic patients in general require fewer treatments in that the volume loss due to the lipoatrophy of aging is much less than HIV-associated lipoatrophy. The slightly greater potential for delayed complications in nonimmune suppressed individuals is discussed in more detail in the complication section of this chapter.

This delayed mechanism of action is important to remember when treating patients with HIV-associated lipoatrophy with PLLA. The current recommendation is

to wait 4–6 weeks after treatment to access the need for additional treatment. This treatment interval can be lengthened as patients approach full correction to maximize time for the correction to occur and minimize the chance of overcorrection. In the original Blue Pacific study, patients appeared to improve clinically in their correction up to 6 months after their last treatment [21].

Well-controlled, sequential, multipatient clinical histology documenting the exact mechanism of action in humans is lacking for PLLA. In the mouse model, Gogolewski et al. [3] showed, at 1 month after PLLA implantation, a microparticle polylactide surrounded by a 100 mm thick capsulation with an increase in vascularity. Histology at 3 months revealed a decrease in cell numbers and capsule thickness of 80 mm. At 6 months capsule thickness had decreased and the surrounding areas were composed entirely of collagen fibers. At 18 months the microparticles were shown to still exist with collagen neogenesis and no signs of inflammation. Lemperle [38] studied the histologic reaction in his own forearm to poly-L-lactic acid. At 1 month there was a fine capsule around the implant. At 3 months the PLLA microspheres were intact, and surrounded by macrophages and lymphocytes. At 6 months the PLLA microspheres were degraded and deformed, and surrounded by macrophages and giant cells. At 9 months the PLLA microparticles completely degraded and there was no detectable scar tissue. This differs somewhat

Fig. 62.6 Biopsy of papule (×100), with H&E stain, showing birefringent particles surrounded by giant cells

from the accepted clinical duration of PLLA in HIVassociated lipoatrophy of 18 months [16, 33] or longer in cosmetic patients [39, 40].

Histology in clinical patients has been confined to biopsies of nodules and papules. These biopsies are rare in that most patients are not clinically bothered by these events in that the vast majority of nodules and papules are palpable, but nonvisible. Therefore, patients rarely opt to have them excised for microscopic examination. In the Blue Pacific study [21], one patient developed an infraorbital papule that the patient elected to have surgically removed at a scheduled blepharoplasty. Histology showed birefringent particles surrounded by giant cells (Fig. 62.6). Beljaards et al. [41] reported similar histologic findings in their report of complications with early, cosmetic use of PLLA. It is unknown, but assumed that nodule/papule formation is related in some way to the generalized, underlying mechanism of action of PLLA.

62.5 Technique

A brief review of facial anatomy or more specifically facial fat anatomy is relevant to understand the changes that occur on the anatomic level with HIV-associated lipoatrophy. An understanding of this anatomy is helpful in planning how and where to place the PLLA for optimum results.

The facial fat can be divided into two layers. The first layer is superficial, between the skin and the

superficialis fascia. Its function is essentially protective and has a fairly even distribution. The thickness of this layer is dependent on total body fat, as well as genetics and nationality. The other layer is deep, under the superficialis fascia. Its principal function is mechanical. This layer is made up of several fat pads, including the intraorbital fat pad, the suborbicularis oculi fat pad (SOOF), the retro-orbicularis oculi fat pad (ROOF), the galeal fat pad, the temporal fat pad, the malar fat pad, and the buccal fat pad. Of these, the temporal, malar, and buccal fat pads are the most commonly affected by HIV facial wasting. However, the pattern is quite variable from patient to patient.

Fat is a well-vascularized tissue with high metabolic activity. In addition to its structural role, fat tissue serves as a reservoir for energy storage. The number of fat cells generally is assumed to be stable after the completion of adolescent growth. Changes in the volume of fatty tissue relate to the size of the cells and their overall lipid content. Cells removed by liposuction or other surgical procedures do not regenerate. In healthy patients, cells shrink with overall weight loss and in fact, may dedifferentiate. However, subsequent weight gain causes redifferentiation of the cells with an increase in volume.

Fat tissue consists of fat cells, which have thin cell membranes enmeshed in a fibrous network. Without the supporting fibers, the cells tend to collapse. An additional supporting network of connective tissue structure creates lobules of fat.

As a side effect of HAART, HIV-associated lipoatrophy may result and can progress toward near complete subdermal facial fat loss in some patients. There is also an associated reduction in the size of the deeper fat pads. This fat loss causes changes in the other soft tissues of the face, leaving atrophic regions of generalized tissue ptosis and loss of the convex contour of the face that represents normal health and youth.

An individual, regional anatomic assessment of the face and the associated underlying fat structures affected by the lipoatrophy better guide the treatment for the optimum benefit from soft tissue fillers. With soft tissue fillers, one is essentially remaking the underlying fatty support to correct the flattening and hollowing that is present and replacing it with the normal contours of the face. Although not replacing fat with fat, correct placement of soft tissue fillers can dramatically reshape the face (Figs. 62.3–62.5).

The technique used to administer PLLA has evolved considerably since its introduction in Europe in 1999. Originally considered a dermal line filler, and not fully appreciating the mechanism of action led to its dilution with the minimal amount of water (1 mL) and placement higher in the dermis. This led to too robust of collagen synthesis with resulting surface irregularities and relatively poor outcomes [41]. Subsequent initial studies [16, 18, 20, 21] of PLLA in HIV lipoatrophy involved dilution to 3 ml with excellent efficacy but still somewhat high rates of adverse events. Further refinement of technique has evolved to greater dilution volumes (6+ ml total diluent), greater dilution times (>24 h), longer treatment intervals (4–6 weeks), and post procedure massage as standards of care when using PLLA. The overlying concept is that as a particulate suspension that stimulates collagen formation gradually, it is important to deliver the PLLA particles in as uniform of a manner as possible.

Factors such as age and the area for correction should be taken into account when planning a treatment regimen [42]. In general, the number of injections per session and total volume of correction is determined by the size of the area to be corrected. For example, if lipoatrophy is particularly severe, a cheek may require as many as 20 injections of 0.1–0.2 ml each [42]. Small marks can be made with a water-sol- uble surgical pen around the area to be injected. Marks should be made with the patient in the sitting position to better assess facial laxity.

There are two types of injection techniques recommended for PLLA, which are known as threading/tunneling and depot. Threading or tunneling is the most appropriate technique for the mid and lower face (cheek, preauricular and malar regions) and should be administered in a cross-hatching type pattern to more evenly cover the desired treatment area and avoid any skip areas [28]. In this area, the needle should be inserted past the deep dermis to the junction with the upper subcutaneous layer at a 30°–40° angle, followed by lowering of the needle to inject parallel to the skin [43]. A change in tissue resistance should be felt as the needle traverses the dermal–subcutaneous junction [24]. Poly-L-lactic acid is injected as the needle is withdrawn in a retrograde fashion, stopping short of the dermis. A recent refinement of technique is the additional placement of PLLA in the supraperiosteal plane where available, such as the midface. The benefit of this being improved efficacy secondary to the

subsequent volume enhancement being only able to move in an anterior or forward direction.

The depot technique is recommended for other areas, such as the temples or upper zygoma. Specifically for the infraorbital area, PLLA injection should be reduced to small boluses of 0.05 ml per injection. The needle should be placed below the orbicularis oculi muscle, depositing the product just above the periosteum [24]. When treating the temples, the needle should be inserted at a 45° angle, with the final product placed below the level of the temporalis muscle fascia. When injecting, it is important to use a reflux maneuver before depositing PLLA to ensure that a blood vessel has not been entered [28].

As a biostimulant, PLLA is dependent on the patient’s own stimulation of fibroblasts to lay down new collagen. Areas of active muscle, such as the orbicularis oculi and facial muscles around the mouth area, cause an increase in fibroblast stimulation. As such, these areas tend to require less product per square centimeter as well as fewer treatment sessions. In general, to avoid overcorrection, a minimal amount of product should be used for each injection (0.1–0.2 ml) and each injection site should be spaced at 0.5–1 cm intervals apart [42]. Of note, deeper, more atrophic areas are corrected with additional treatment sessions rather than additional product at the initial treatment, to avoid an overabundant formation of collagen in that area. Injections are carried out with a 25or 26-gauge needle and the treated area should be massaged following every two to three injections [42]. Patients should also be advised to massage the treatment area periodically for several days after treatment. Lidocaine may be added to the product immediately prior to use to increase patient comfort.

62.6 Longevity

When discussing longevity with any reconstructive treatment, it is important to clarify between absolute duration of action and more importantly, clinical duration of action. That is, specifically, the time to clinical retreatment. This is especially important in patients with HIV facial lipoatrophy as the psychological meaning to patients of even a mild decrease in correction of the normal facial contours is significant. Naturally, this threshold will vary from patient to patient.

This concept becomes important when analyzing various long-term studies using PLLA in facial lipoatrophy. In the VEGA study [16], patients were not allowed interval treatments for 96 weeks. At the end of the study, patients were still visually improved compared to baseline. Since this was one of the pivotal studies used as part of the US FDA approval of PLLA, the product labeling for duration of PLLA effect is that the product “persists” for up to 2 years. In the other pivotal study evaluated by the US FDA, Moyle et al. [18] found that 14 of 27 patients had received additional PLLA treatments between the end of the initial study (6 months) and the long-term follow up visit at 18 months. It should be noted that in 10 of these patients, treatment was in areas not previously treated, which highlights the fact that clinically, physicians treating patients with facial lipoatrophy are dealing with possible continued fat loss. Patients should be counseled as such when undergoing treatment with any substance. In addition, this study used a fixed dosing scheme and therefore some patients may not have been fully corrected after the initial treatment series. Lafaurie et al. [17] in a 2005 study found that statistically, the probability of reinjection 15 months after the end of treatment was 45% as assessed by the Kaplan–Meier method. Of the 61 patients reported by Burgess [8], following fixed three treatments, significant improvement and dermal thickening was retained in 37 patients for 6 months, 1 year for 10 patients, 18 months for 9 patients, and 2 or more years for 5 patients.

In the longest-term follow-up study (36 months) to date on PLLA and HIV facial lipoatrophy, the extension study of the original Blue Pacific study examined the 75 patients who returned for measurement at month 12 [33]. PLLA was reconstituted with 5 ml of sterile water 2 h prior to injection and was injected into target treatment areas in the deep dermal/subcutaneous layer. A total of 1–10 ml of PLLA was given via a crossfanning injection technique; utilizing a 25-gauge 1.5-in. needle, 0.1–0.2 ml threads of PLLA were placed per injection in a retrograde manner. Similar injections were then placed at approximately 90° to the original injections in the treatment areas. No more than 10 ml of reconstituted PLLA was injected at any single treatment session. Patients were treated at 5-week intervals (maximum deviation of 10 days) until full correction was obtained. Patients could receive a maximum of 12 treatment sessions over the 24-month study period if need was mutually agreed on by the treating

physician and the patient. Caliper skin thickness was measured, and serial digital photographs were taken before each subsequent treatment session to assess the continued efficacy of PLLA.

Of 75 patients, 65 (63 male and 2 female) required retreatment during the study period and consented to participate in the retreatment study. Of the ten eligible patients who did not enter the retreatment study, nine continued to have persistent correction after 36 months and did not require retreatment during the extension phase, and one patient was treated at 30 months by his local physician.

Table 62.5 demonstrates the study results according to severity of original (presenting) facial lipoatrophy by the James scale: 1 (n = 8), 2 (n = 11), 3 (n = 32), and 4 (n = 14). The time to first retreatment varied by the original James scale score: 1 (21.4 months), 2 (15.7 months), 3 (14.0 months), and 4 (13.0 months). Patients with mild (James scale score 1) facial lipoatrophy had a mean of 1.9 retreatments, whereas those with moderate to severe facial lipoatrophy required more retreatments: for James scale score 2, 3, and 4 the mean number of retreatments were 3.4, 4.4, and 4.8, respectively. Approximately 50% of patients (n = 34) required

Reproduced with permission from Mest and Humble [33]

aChange from end of treatment in the Blue Pacific study to time of first retreatment

bIncludes one patient who presented for initial retreatment with areas of overcorrection/irregular growth. Exclusion of this patient yields −0.2 mm