Trichoscopy of Pressure-Induced Alopecia and Alopecia Areata: A Comparative Study.

Background: Pressure-induced alopecia is an uncommon type of alopecia. It can occur in both scarring as well as non-scarring form and occurs due to ischemia resulting from prolonged head immobilisation during surgery or hospitalisation. The patchy hair loss generally involves convexities of scalp specially vertex and occiput. The hair loss is usually noticed 3 -28 days after the inciting event and regrowth of hair occurs between 1 - 4 months. Objective: To describe trichoscopic features of pressure alopecia and compare it with the closest differential, alopecia areata. Methodology: It is a retrospective observational study. Trichoscopic features of six cases of pressure alopecia seen during the study period were compared with alopecia areata and analyzed using appropriate statistical methods.
Results: The study had 30 cases, six cases of pressure alopecia and 24 cases of alopecia areata. The mean age of patients with pressure alopecia and alopecia areata was 45.16 and 29.08 years respectively. Comedone- like black dots, black dots and area of scarring were statistically significant for pressure alopecia while exclamation mark hairs were significant for alopecia areata.
Conclusion: Trichoscopy is a non-invasive test for diagnosis of alopecia and "Comedone-like black dots" are unique trichoscopic feature of pressure alopecia. Copyright:

INTRODUCTION

Pressure-induced alopecia is an uncommon type of alopecia. It can occur in both scarring and nonscarring forms and occurs due to ischemia resulting from prolonged head immobilization during surgery or hospitalization. It presents as a localized form of alopecia and is confused with other forms of alopecia, especially alopecia areata (AA), if temporal relation with inciting event is not forthcoming and physician is not aware of such an entity.

Pressure alopecia (PA) is also known as postoperative alopecia and is usually seen in adults and rarely in children. It has been reported after prolonged surgical procedures (cardiothoracic, gynecological, reconstructive, genitourinary, and neurosurgical) and prolonged stay in the intensive care unit (ICU). It has also been reported after application of electroencephalogram (EEG) electrodes, orthodontic headgear, and use of cervical collars.[1] The patchy hair loss generally involves convexities of the scalp, especially vertex and occiput. The hair loss is usually noticed 3–28 days after the inciting event, and the regrowth of hair occurs between 1 and 4 months. Depending on the degree of pressure-induced tissue ischemia, a patient can develop nonscarring or scarring alopecia. Milder ischemia results in nonscarring alopecia, whereas prolonged ischemia results in ulcer formation and resultant scarring alopecia.[2]

METHODOLOGY

It is a retrospective observational study. We analyzed trichoscopy of six cases of PA and compared it to trichoscopy of AA during study period. The trichoscopic images were independently analyzed by two experienced dermatologists (SN and DV), and findings were recorded in pro forma. The images were evaluated for the following trichoscopic features: comedone-like black dots, broken hairs, yellow dots, black dots, miniaturized hairs, exclamation mark hairs, and area of scarring. The data were entered in an Excel sheet. Continuous variables were expressed as mean and standard deviation. Qualitative variables were expressed as frequency and percentage. Fisher's exact test or Chi-square test was used for categorical variables. P < 0.05 has been taken as statistically significant. The data have been analyzed using StataCorp. 2013. Stata Statistical Software: Release 13. College Station, TX: StataCorp LP.

RESULTS

The study group consisted of 4 males and 2 females, whereas the control group consisted of 15 males and 9 females. The mean age of patients in the study group and the control group was 45.16 and 29.08 years, respectively. The occipital scalp was the site of alopecia in 5 out of 6 cases in the study group whereas in 1 case alopecia involved temporal region. Three cases occurred after prolonged ICU stay, whereas three cases occurred after surgery (one each after cardiac surgery, neurosurgery, and spine surgery) [Figure 1].

Figure 1

The typical site of pressure alopecia on occipital scalp

Comedone-like black dots were unique features for PA and were seen in 66% (4/6) of patients and none of the patients with AA (P = 0.0005) [Figures 2 and 3]. Black dots and area of scarring [Figures 4 and 5] are more commonly seen in PA, whereas yellow dots and exclamation mark hairs [Figures 6 and 7] are more commonly seen in AA. Miniaturized hairs [Figures 2 and 3] are seen in both PA and AA. The results are tabulated in Table 1.

Figure 2

Polarized dermoscopy (DermLite DL4, ×10) of pressure alopecia shows broken hairs (blue arrow), comedone-like black dots (blue star), yellow dots (red circle), and miniaturized hairs (yellow arrow)

Figure 3

Polarized dermoscopy (DermLite DL4, ×10) of pressure alopecia shows numerous yellow dots (red circle), comedone-like black dots (blue star), and miniaturized hairs (yellow arrow)

Figure 4

Polarized dermoscopy (DermLite DL4, ×10) of pressure alopecia shows yellow dots (red circle), miniaturized hairs (yellow arrow), and white homogenous area with surrounding erythema suggestive of scarring (orange star) in case of pressure alopecia

Figure 5

Polarized dermoscopy (DermLite DL4, ×10) of pressure alopecia shows yellow dots (red circle), black dots (green circle), comedone-like black dots (blue star), and area of ulceration (blue arrow) in case of pressure alopecia

Figure 6

Polarized dermoscopy (DermLite DL4, ×10) of alopecia areata shows yellow dots (red circle), black dots (green circle), exclamation mark hairs (blue arrow), and broken hairs

Figure 7

Polarized dermoscopy (DermLite DL4, ×10) of alopecia areata shows numerous black dots (blue circle) and yellow dots (red circle)

Table 1

Comparison of trichoscopic features of pressure alopecia and alopecia areata

Serial number	Parameters	Alopecia areata (n=24)	Pressure alopecia (n=6)	P
	Age (mean±SD)	29.08 (12.0)	45.16 (4.24)
	Sex (male: female)	1.4:1	2:1
	Trichoscopic feature
A	Comedone-like black dots	0/24	4/6	0.0005
B	Broken hairs	7/24	3/6	0.37
C	Yellow dots	12/24	6/6	0.0568
D	Black dots	5/24	5/6	0.008
E	Miniaturized hairs	22/24	6/6	1
F	Exclamation mark hair	18/24	0/6	0.0016
G	Area of scarring	1/24	3/6	0.0181

SD – Standard deviation

DISCUSSION

PA is a relatively uncommon form of alopecia and is seen after surgery or prolonged immobilization. The most common site for PA is occiput as the patient lies supine and prolonged immobilization can lead to tissue ischemia in the convex area of the scalp when the tissue gets compressed between calvarium and surface. In 1960 and 1964, Abel et al. reported alopecia in patients after prolonged surgery. The median time for alopecia to appear was on the 15th day (3 to 30 days), and the authors ascribed this alopecia to ischemia resulting from steady pressure of head against operating table.[34] In our study, five out of six patients had alopecia on occiput, whereas one patient had temporal alopecia, who underwent neurosurgery on the opposite side.

The diagnosis of PA is based on a typical history of prolonged surgery or immobilization and clinical features such as presence of alopecia in occiput and ulceration or scarring. Rarely, PA can occur in other settings, and it has been reported after less intense pressure application such as head strap application, exercise on balance beam, application of orthodontic appliances, and EEG electrodes.[567]

Similarly, it has also been reported in neonates due to prolonged second stage of labor, birth trauma, or ventouse-assisted delivery.[89] The pressure required to cause ischemia and resultant PA may be variable in different individuals.

PA is reversible in majority of the cases, and hair regrowth appears within months. Loh et al. in their series reported that operation time is the most critical factor in determining reversibility of hair loss and duration of more than 10 h in general anesthesia was associated with scarring alopecia. In our study, the area of scarring was noted in three cases (50%), but the exact duration of surgery was not known.

Hanly et al. reported the role of apoptosis in PA. They noticed multiple catagen hairs and apoptotic bodies in histopathology specimens of PA and hypothesized that tissue hypoxia terminates anagen and hairs enter in catagen. The reversibility of hair loss depends on the degree of ischemia with a milder degree of ischemia resulting in nonscarring alopecia and regrowth within 120 days, whereas prolonged ischemia results in ulceration, scarring, and permanent hair loss. They also noticed pigment casts in histopathology and compared it to other cases of alopecia and noted the presence of both apoptotic bodies and pigment casts in AA and trichotillomania.[10]

Trichoscopy may help in diagnosis and differentiation from other commonly seen alopecia like AA, especially when the history of inciting factor is not elicited. The description of trichoscopic features of PA in literature is scant and overlaps greatly with AA which is its closest differential diagnosis. Trichoscopic features are reflection of histopathology and similar to histopathology, overlapping features on trichoscopy are common. Rather than a single trichoscopic feature, a constellation of features points to a specific diagnosis. The presence of black dots, yellow dots, and thin hairs and the absence of exclamation mark hairs, corkscrew hairs, and comma hairs suggested a diagnosis of PA in previous studies.[21112] In our study, we found a unique trichoscopic feature “comedone-like black dots” in 66% of patients (4/6) and in none of the cases of AA. Exclamation mark hairs were seen in 75% (18/24) of cases of AA and none of the cases of PA. These two features were mutually exclusive trichoscopic features for the condition and if found and help in diagnosis or excluding other conditions. Other trichoscopic features such as black dots, yellow dots, miniaturized hairs, broken hairs, and area of scarring are found with varying frequency in either condition.

CONCLUSION

PA is an uncommon condition and should be suspected in the setting of prolonged surgery or immobilization and occipital alopecia. Comedone-like black dot is a unique trichoscopic feature which can help in rapid identification of the condition and differentiation from AA.

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Conflicts of interest

There are no conflicts of interest.