Biomedical Engineering Reference
In-Depth Information
(
A
)
(
B
)
Figure 5.13
(
A
) Incorrect use of treatment parameters (fl uence too high for particular skin type) caused epidermal damage with subsequent superfi cial erosions.
(
B
) Complete healing with postinfl ammatory erythema and initial postinfl ammatory hyperpigmentation at 2 weeks.
imperative (Fig. 5.13). It is also more common in patients with a
tan. Herpes simplex outbreaks are uncommon but may occur.
There is a higher risk among patients with a previous history
of herpes simplex and when the perioral, pubic, or bikini area
are treated. The risk of bacterial infection is extremely low.
However, it may occur following epidermal damage.
Folliculitis may occur in areas treated after excessive sweat-
ing or vigorous exercise. An additional risk is posed by swim-
ming or using a hot-tub around treatment sessions. The most
common side effects are transient pigmentary changes, such as
hypopigmentation (Fig. 5.14) or hyperpigmentation (Fig. 5.15).
It can be prevented if the appropriate treatment fl uences
are chosen for a certain skin type. This problem is mostly seen
in patients with darker skin types or when patients have had a
recent tan (49-52). Permanent pigmentary changes are unlikely
except in dark-skinned individuals (53).
For those patients with Fitzpatrick skin type IV or greater, of
Mediterranean, Middle Eastern, Asian or South Asian descent,
or hirsutism in the “beard” and lateral face distribution,
treatment with laser may result in paradoxical hypertrichosis
(21-24) (conversion of vellus hairs to terminal hairs). The
incidence of paradoxical hypertrichosis is not clear, although
the aforementioned factors are thought to place the patient at
risk for this poorly understood phenomenon. Nonetheless,
this rare phenomenon has also been observed on the back of
Caucasian males when treated with hair removal lasers. One
mechanistic explanation for paradoxical hypertrichosis is that
the scattering of photons that occurs at the periphery of a laser
beam lowers the effective fl uence at the edges and that this low
level of energy at the beam periphery may actually be stimula-
tory to hair growth rather than resulting in thermal destruc-
tion of the hair follicle stem cells.
Scarring is unlikely except in cases of overaggressive treatment,
failure to protect the epidermis, or postoperative infection.
Loss of freckles or lightening of tattoos or pigmented lesions
is not uncommon. Patients should be aware of this possibility.
Temporary or permanent leukotrichia has been said to
develop following laser or IPL hair removal (54). This fi nding
may be explained by the difference in the TRTs of melanocytes
and germinative cells. The light absorbed and the heat pro-
duced by melanin may be suffi cient enough to destroy or
Figure 5.14
Treatment of recently tanned skin caused hypopigmentation.
impair the function of melanocytes but insuffi cient to damage
the hair follicle cells.
A case of lichen planus triggered by long-pulsed ruby laser
treatment for hair removal has been reported (55). Logic
would suggest that all patients with a history of skin diseases
known to show a Koebner phenomenon, such as psoriasis vul-
garis, vitiligo, lichen planus, and Darier disease, should be
informed about this possible adverse effect of treatment; clini-
cally this is rarely seen.
Livedo reticularis (Fig. 5.16) (56), intense pruritus, and urti-
caria (57) have been reported, including a case of intense swell-
ing and erythema. The pathophysiology of these phenomena is
not known. Management included topical corticosteroids,
antihistamines, and discontinuing treatment. Several cases of
induction of hair growth following LHR in young female
patients with darker skin types have been reported (Fig. 5.11)
(21-24). Two different phenomena have been observed: Either
conversion of fi ne vellus hair to dark, coarse terminal hair at
the site of treatment or induction of growth of long fi ne hairs
