Efficacy of Short Pulsed 1064 nm Nd-YAG Laser Versus 10600 nm Fractional CO2 Laser in Treatment of Striae Alba

Overview

Striae alba is a clinical variant of striae distensae characterized by focal dermal collagen loss and thinning of elastic fibers. Carbon dioxide (CO2) laser is an ablative laser modality that ablates defective collagen and stimulates new collagen formation. Neodymium-Doped Yttrium Aluminum Garnet (Nd-YAG) laser is a non ablative modality that results in stimulation of collagen formation through dermal heating. High frequency skin ultrasound is a rapid and non-invasive tool for measurement f skin thickness and can be used for this purpose.

Striae distensae (SD) are skin disorders characterized by linear parallel edematous plaques that evolve into atrophic depressions in areas of dermal damage. They commonly develop on sites of skin stretching including thighs, arms and gluteal areas in males and additionally breasts in females, abdomen in case of pregnant females or intertreginous sites in case of glucocorticoids therapy and cushing disease. All result in pathological changes comprising early dermal edema and perivascular lymphocytic infiltrate (manifest clinically as striae rubra) and end by epidermal thinning, flattening of dermal papillae, thinning of dermal collagen bundles and abundance of abnormally thinned and branched elastic fibers (manifest clinically as striae alba). Various preventative and active treatment modalities for SD which were proven beneficial included: topical therapeutics like topical retinoids, energy based devices like fractional radiofrequency (FRF) and light therapy including both non-coherent light like intense pulsed light therapy and coherent laser devices like fractional ablative CO2 laser and non-ablative Nd-YAG laser. However obtaining a single effective treatment is still a challenge especially in absence of randomized control studies for some modalities and low level of evidence (LOE) for others. Fractional ablative CO2 laser creates columns of focal dermo-epidermal tissue loss known as (microablative columns) with thermal damage, hemostatic effect and incomplete coagulation of tissues. This ablation of dermal tissues (including collagen and elastin) has the potential for stimulation of new tissue formation in SD. The efficacy of fractional CO2 laser in treatment of striae alba was discussed in various studies. In a LOE 4 retrospective study involved 27 patients each received one session of fractional ablative CO2 laser (at 10 mJ using ultrapulsed deep FX mode with spot diameter 1-10 mm) ; (7.4%) of patients have shown (\>75 %) improvement, (51.9%) have shown (51 - 75%) improvement, (33.3%) have shown (26 - 50%) improvement and (7.4%) have shown (\<25%) improvement. Another comparative study between both fractional ablative CO2 laser and non-ablative Erbium-glass laser with LOE=2 conducted on 22 patients using three sessions with four weeks interval. Fractional CO2 laser parameters were set to (fluence = 40-50 mJ, 75-100 spots/Cm2 spot density and spot size = 8x8 mm in a static mode). Results have shown marked clinical improvement in 90.9% of patients from both modalities with no statistically significant difference between both. A third comparative study (LOE=2) between fractional CO2 laser, FRF and combination between both included 30 patients using (fluence=700-1000 mJ and 0.7 mm spot density) for the fractional CO2 laser. Clinical improvement was noticed in all three groups with best results for the combination group. This result was supported by histopathological evidence in the form of increased epidermal and collagen thickness in analysis of biopsies retrieved from two patients. A Fourth comparative study (LOE=2) between combination of fractional ablative CO2 laser and microneedle FRF versus only microneedle FRF conducted on six patients using five sessions with four weeks interval. Fractional CO2 was conducted using (fluence = 14-18J/Cm2 and ablation depth = 400-600 micrometers in ultrapulsed mode using two passes). A statistically significant better result was noticed in the combination group with overall greater reduction in mean surface area of SD pointing to an additive positive role for fractional CO2 laser. A fifth comparative study between fractional CO2 laser versus combination of topical glycolic acid and tretinoin (LOE=2) conducted on six patients through five sessions with two to four weeks interval. Fractional CO2 was set to (fluence = 14-18 J/Cm2 in ultrapulsed mode). Statistically significant better results were noticed in fractional CO2 laser group with reduction in mean surface area of SD. Neodymium-Doped Yttrium Aluminum Garnet (Nd-YAG) laser is another successful therapeutic modality and is characterized by its safe profile compared to other lasers. Long pulsed Nd-YAG laser results in a non-ablative dermal heating with intact overlying epidermis which has shown a potential for dermal collagen remodeling in histological sections (14). El Saie and his colleagues compared the efficacy of two fluences (75 J/Cm2 and 100 J/Cm2) of Nd-YAG using (spot size = 5 mm, pulse duration = 15 ms and frequency = 1 Hz) in the treatment of SD (both striae alba and rubra patients). Improvement was noticed in both types of striae. However, patients with striae alba showed better improvement in the higher fluence group. Increased dermal collagen and elastin were supported by histopathological evidences for biopsies retrieved from six patients. Nevertheless, other studies pointed to higher effectiveness in cases of striae rubra than striae alba which suggests an additional role for Nd-YAG laser in targeting dermal vascular changes in SD. There were no previous attempts for comparing fractional ablative CO2 laser and long pulsed non-ablative Nd-YAG laser for treatment of striae alba patients. In a recent systematic review, a LOE=2 comparative study was conducted between 2940nm Erbium - Yettrium Aluminum Garnet (Er-YAG) ablative laser and non-ablative 1064nm Nd-YAG laser for treatment of patient with striae alba. Each group received three sessions with four weeks interval. Parameters were set to (power= 3.2 J and spot size= 7mm in a short pulsed mode) for Er-YAG laser and (fluence= 50 J/Cm2, spot size= 50 ms and pulse duration = 50ms) for Nd-YAG laser. Both groups have shown poor results. Overall conclusion from systematic review was that ablative lasers as an option for treatment of SD were less well-tolerated by patients and results were more variable among studies than non-ablative lasers. Clinical evaluation of patients shall be determined by Davey's modified score for the number and severity of the striae in the affected area, both before and after treatment to determine the degree of improvement or worsening. Objective evaluation of the efficacy of different therapeutic modalities is highly important to determine the optimal management. High frequency skin ultrasound (HFSU) is a rapid and non-invasive tool for measurement of skin thickness and can be used for this purpose, It is an ultrasound-based apparatus that emits ultrasound waves through a transducer in high frequencies that vary according to the designated visualized structure or tissue. In skin, 18 MHz devices are used primarily for dermal component imaging and 50-100 MHz devices for epidermal component imaging. Using bimodal devices is a more advanced option for visualization of ultrastructures of the dermis like collagen, elastic fibers and dermal ground substance. Statistical analysis shall be done after study completion to determine the significance of the outcome parameters.