Download Polarizable elements in scabies infestation: a clue to diagnosis

Copyright © 2012 John Wiley & Sons A/S
J Cutan Pathol 2013: 40: 6–10
doi: 10.1111/cup.12035
John Wiley & Sons. Printed in Singapore
Journal of
Cutaneous Pathology
Polarizable elements in scabies
infestation: a clue to diagnosis
The diagnosis of scabies infestation is straightforward in cases where
mite parts are largely visible; however, mites are often not captured in a
specimen’s planes of section. Polariscopic examination is a fast and
simple adjunctive diagnostic tool to light microscopy. We describe the
unique polariscopic findings in scabies infestation. Two cases of crusted
scabies and eight cases of typical scabies were subjected to polariscopic
examination. Diagnostic mite parts were visualized in at least one
section in all cases. Attached and detached spines as well as scybala
(fecal material) are polarizable. Specifically, spines show a polarizable
outer sheath with dark central core while scybala show peripherally
concentrated, stippled birefringence. Similar stippled birefringence is
visible within the gut of some mites whereas significant birefringence is
not appreciated in other mite parts. These results suggest that
polariscopic examination is a helpful clue in the diagnosis of scabies
infestation, especially in cases where the body of the mite is not
visualized.
Keywords: demodex, polarize, scabies
Foo CW, Florell SR, Bowen AR. Polarizable elements in scabies
infestation: a clue to diagnosis.
J Cutan Pathol 2013; 40: 6–10. © 2012 John Wiley & Sons A/S.
Human scabies is a pruritic skin eruption caused by
the infestation of the eight-legged mite Sarcoptes scabiei
var. hominis. Transmission occurs via close direct
human contact1 or can be indirectly acquired via
fomites. The entire life cycle of scabies is completed
within the human epidermis with cutaneous lesions
associated with pruritus developing as a result
of the host immune response to the mite or its
byproducts. Diagnosis is most often confirmed in the
clinic by identification of mites or mite byproducts
in skin scrapings by mineral oil light microscopic
examination. Scabies can be diagnosed by skin
biopsy if mite parts, eggs or fecal pellets (scybala)
are identified. Kristjansson et al. have also described
pathognomonic pink ‘pigtail-like’ structures attached
to the epidermis that are thought to represent
abandoned egg cases.2 As the number of mites on
the host is typically small, the chance of making
a definitive diagnosis by biopsy is relatively low,
Chong Wee Foo, Scott R.
Florell and Anneli R. Bowen
Department of Dermatology, University of
Utah, Salt Lake City, UT, USA
Anneli R. Bowen,
Department of Dermatology, University of Utah,
30 N. 1900 E. Suite 4A330, Salt Lake City, UT
84132, USA
Tel: +1 801 581 6465
Fax: +1 801 581 6484
e-mail: [email protected]
Accepted for publication September 27, 2012
and often the diagnosis must be inferred based on
non-specific features including epidermal spongiosis
with superficial perivascular or diffuse infiltrates of
lymphocytes, histiocytes and eosinophils.3
Polarized light microscopy is a simple and
inexpensive adjunctive method of examining microscopic specimens. We demonstrate unique polariscopic features in scabetic infestations that can
facilitate making a histopathological diagnosis.
Methods
Ten cases of human scabies were retrieved from the
dermatopathology archives at the University of Utah,
Department of Dermatology and retrospectively
reviewed. Two crusted and eight typical scabies
specimens were examined with hematoxylin and
eosin stain under light microscopy and with an
Olympus BX41 U-POT Japan polarizer (Olympus
Corporation, Tokyo, Japan). A histopathological
6
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Polarizable elements in scabies
A
B
Fig. 1. Scabies mite with longitudinally sectioned attached and detached spines (A) showing central dark core and peripheral birefringence
with polarized light (B). Internal scabola shows stippled birefringence. The stratum corneum also shows faint pink-white birefringence.
diagnosis of scabies was made in all ten cases because
of the presence of visible mite parts under light
microscopy. For comparison, additional non-scabies
specimens harboring the relative of scabies, Demodex,
were subjected to polariscopic examination.
Results
Under polariscopic light, scabetic spines are circular
on cross-section and show a dark center with
peripheral birefringence (Figs. 1 and 2). Spines
measure up to 50 μm in length and 1–10 μm in
width. Scybala show a stippled birefringence that is
concentrated peripherally. Even scybala retained in
gut show similar stippled birefringence (Figs. 1 and
2). In the four cases, polarizable spines and scybala
were visualized in sections that lacked a visible mite
body. Other mite body parts and pink ‘pigtails’ do
not polarize.
With light microscopy alone, mite parts, scybala,
attached and detached spines and pink ‘pigtails’
were visualized separately or in combination in the
stratum corneum of all 10 scabies cases. Mite bodies
were visualized in at least one profile in nine cases.
Polarizable fecal pellets (scybala) within the mite or
external to the mite were visualized in six cases.
Spines were visualized in all 10 cases, being attached
to mites in 9 cases and detached in 6 cases. Pink
‘pig-tails’ were visualized in two cases. In four cases,
there were profiles where polarizable elements were
the only evidence of scabies infestation, while other
profiles on the slide showed diagnostic mite body
parts (Fig. 4). Results are summarized in the Table 1.
Demodex mites are common inhabitants within
hair follicles, and as relatives of scabies, we studied
their polariscopic features for comparison. On light
microscopy small, granular, brown, inclusions were
identified within the abdomen of Demodex mites, but
A
B
Fig. 2. Scabies mite and scybala with routine light microscopy (A)
and polarized light microscopy (B). Scabies mite body (1), internal
fecal material (2), external scybala (3), attached spine (4) and detached
spines (5).
not in their surroundings. These inclusions showed
stippled birefringence similar to scabies fecal material
and may represent Demodex fecal material (Fig. 3).
In addition, tiny claw-like projections from Demodex
leg tips are faintly polarizable. The polariscopic
features of Demodex were easily distinguished from
polarizable scabetic parts because of disparities in
size, shape and location.
Discussion
Polarized light microscopy is a quick, simple and
inexpensive assistive method of examining specimens
in cutaneous pathology. Foreign body material such
as suture fragments,4 talc,5 starch,6 plant material,7
cryptococcal organisms8 and cosmetic fillers9
are polarizable. Likewise, endogenously produced
crystals including urate, calcium pyrophosphate
and oxalate are also birefringent with polarized
light microscopy. Amyloid deposits are identified
with the Congo red staining method combined
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Foo et al.
A
B
C
D
Fig. 3. (A and B) Demodex mite with intraabdominal polarizable material (arrows) and (C and D) polarizable claw-like projections on mite’s
legs (arrows).
Table 1. Number of scabies cases demonstrating specific diagnostic
features out of a total of 10 cases
Polarizable or
histopathologic feature
Polarizable spines
Attached spines
Detached spines
Both attached and detached spines
Polarizable scybala
External scybala
Internal scybala
Both internal and external scybala
Mite body visible in at least one profile
Pink ‘pigtails’ (abandoned egg cases)
Polarizable elements the only diagnostic
feature in at least one profile (although mite
body visualized elsewhere on the slide)
Number of cases
with this feature
10/10
9/10
6/10
5/10
6/10
3/10
6/10
3/10
9/10
7/10
4/10
with polariscopic examination and normal skin
structures including hair, collagen bundles, the
stratum corneum and even intracellular keratin
tonofilaments are polarizable to varying degrees.10
The polariscopic features of scabies mites became
a topic of study after analysis of a scalp biopsy
from a 51-year-old woman submitted with clinical
information of ‘scalp itch’. The specimen consisted of
a thick hyperkeratotic stratum corneum containing
brown, apparently foreign material that was strikingly
birefringent (Fig. 4A,B). This brown material was
determined to be scybala once leveled sections
identified mite body parts and a conversation with the
clinician indicated that scabies was suspected because
the patient’s son was affected. Further investigation
revealed that scabies spines are also polarizable.
All scabies cases in our series showed birefringent elements when examined under polarized light
microscopy. These polarizable elements consisted of
attached and detached spines as well as scybala,
while mite bodies and pink ‘pig tails’ (egg cases) were
not polarizable. Detached spines are difficult to see
with traditional light microscopy but are very easily
visualized when polarized. In fact, polarizable elements were identified in the absence of other nearby
mite parts in four of our cases, and served as the only
diagnostic evidence of scabies in these profiles (Fig. 4).
8
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Polarizable elements in scabies
A
B
C
D
E
F
G
H
Fig. 4. Four cases demonstrated sections where polarizable scabies
parts were the only diagnostic feature, although mite bodies were
confirmed elsewhere on the slide. Polarizable scybala are seen in
case 1 (A and B) and case 3 (E and F). Case 2 (C and D) and case
4 (G and H) show polarizable detached spines. Case 1 represents
crusted scabies and case 2, 3 and 4 are classic scabies.
S. scabiei is recognized by its oval, ventrally
flattened body, four pairs of legs and numerous
cuticular spines.11 The female scabies mite measures
about 0.3–0.5 mm, and lays between 60 and 90 eggs
during its adult lifespan. The entire 30-day life cycle
of the scabies mite is completed within the human
epidermis12 where it is thought to feed on lysed
epidermal material. Demodex mites are intrafollicular
parasitic mites commonly encountered as an incidental finding in skin specimens from sebaceous regions.
While not typically confused with scabies because of
their elongated bodies, different distribution (head
and neck as opposed to trunk and extremities) and
intrafollicular habitat, Demodex mites are related to
S. scabiei and share some histopathological features.
Small claw-like projections from Demodex legs are
polarizable but are tiny in comparison with scabies
spines (Fig. 3). In addition, small, birefringent
concretions are present within the abdomen of
Demodex mites that may represent fecal material
given their similarity to scabies scybala. In contrast
to scabies, these polarizable concretions were only
identified within the body of the Demodex mite and
not in its surroundings. Like scabies, Demodex feed on
corneocytes, although their diet also includes sebum.
Corneocytes of the stratum corneum are polarizable
and Gonzalez-Serva et al. have reported polarizable
crystals in sebum13 raising the possibility that the
intraabdominal birefringent material in both scabies
and Demodex scybala may be related to an intrinsic
characteristic of the mites’ diet. The polariscopic
features of other parasitic organisms such as tungiasis
or larva migrans have not been described, although
the mouth hooks, larval spiracles and spines of the
intradermal parasite, Dermatobia hominis, are reportedly polarizable.14 As the size and location of these
parasites are very different than scabies, they are not
typically considered in the same differential diagnosis.
Many foreign polarizable materials may be present
in or on the stratum corneum including talc,
fiberglass15 and titanium,16 and as many pathologists
have noted there are a myriad of non-specific
polarizable fragments on slides, on the surface of the
skin and within serum crust. All of these may present
potential pitfalls when using polarized light to assist
in the diagnosis of scabies. However, familiarity with
the specific polariscopic features, size and location
of scabies elements should help the pathologist
avoid making an incorrect diagnosis. Scybala are
rounded, amorphous masses with stippled, peripheral
birefringence while spines are small and delicate,
measuring 1–10 μm in diameter and up to 50 μm in
length, and show polarizable outer cortex with a dark
central core that is visualized as birefringent parallel
lines. Both appear in cavities within the stratum
corneum. Polarizable material sitting on the surface
of the stratum corneum is most probably non-specific.
Given the small number of mites that infest the
skin in most cases of human scabies, it can be
difficult to actually capture a mite within a skin
biopsy. Moreover, mite parts and scybala can easily
be overlooked with traditional light microscopy. The
addition of polariscopic examination provides a rapid
and convenient adjunctive tool in the identification
of scabies infestation and can increase the probability
of making the correct diagnosis.
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