Dermoscopy as a Tool to Differentiate Reactive Arthritis from Psoriatic Arthritis

Sir,

Reactive arthritis (ReA) is a seronegative inflammatory arthritis that may show mucocutaneous lesions in up to 50% of patients. The typical cutaneous findings include psoriasiform plaques, pustulations, and crusting, which may appear before or after the onset of the oligoarthritis.[1] In the presence of cutaneous lesions, differentiation of ReA from psoriasis with psoriatic arthritis (PsA) is important because of differences in the treatment strategies and overall prognosis.

This was a cross-sectional study that compared the dermoscopic features of age-matched ReA (n = 6, males = 6, mean age = 25 years, diagnosed as per American College of Rheumatology criteria) and PsA (n = 15, males = 12, females = 3, mean age = 31 years, diagnosed as per Classification Criteria for Psoriatic Arthritis criteria; 5 had cutaneous lesions of pustular psoriasis) patients. All patients were seronegative for HIV infection.

Dermoscopy of ReA patients on Dermlite DL4; 3Gen, CA; polarized mode, at 10× magnification [Figure 1a and b] showed closely placed islands of brownish plates separated at their edges from the surrounding flaccid pustules, simulating a “double-edged scale.” Active pustulations were noted at the periphery of these brownish crusts, removal of which revealed regularly arranged glomerular and dotted vessels on a background of erythema, akin to psoriasis. Silvery white scales were noted in the older lesions. PsA patients showed regularly arranged red dots and silvery-white scales. Both micro- and macro-pustules were seen in cases of pustular psoriasis. However, islands of brownish plates with “double edged scales” were typically lacking [Figure 1c and d]. Dotted vessels and glomerular vessels were seen variably in both ReA and PsA. Statistical analysis (Fisher exact test) revealed islands of brownish plates with double-edged scales as specific dermoscopic findings in ReA [Table 1]. Histopathology of the cutaneous lesions in both conditions showed psoriasiform dermatitis, and we were unable to delineate these entities based on histology alone [Figure 1 (e and f)]

Figure 1.

(a) Dermoscopic features of cutaneous lesions of reactive arthritis. Dermoscopy of early lesion shows white-yellow blotches of pus (blue star) that has dried at the center to leave brownish plate/crust (white star). Mature lesions with islands of brownish plates (black star) with double-edged scales (black arrows) are also evident. (b) Another case of reactive arthritis showing brownish plates (star) detached at periphery (arrows) with surrounding pustulation (circle) forming a double-edged scale. (c) Dermoscopic features of psoriasis/pustular psoriasis in psoriatic arthritis patients. Dermoscopy shows yellowish white randomly placed scales (asterisk) with minute pustules (arrow) distributed diffusely in the lesion. Dotted vessels are highlighted with a circle. (d) Dermoscopy of pustular psoriasis shows silvery white to yellowish scales (white arrow) on an erythematous background with macropustules (black arrow) and dotted vessels (circle); (Dermlite DL4; 3Gen, CA; polarized mode, 10 × magnification). (e and f) Histopathological image of lesion from reactive arthritis showing marked parakeratosis, regular acanthosis with club shaped rete ridges, neutrophilic exocytosis and focal neutrophilic micro-abscesses (Hematoxylin and Eosin; 100× (e) and 200× (f)).

Table 1.

Comparison of dermoscopic features observed in cutaneous plaques of reactive arthritis and PsA

Dermoscopic findings	Reactive arthritis	Psoriatic arthritis	P
Background
Erythema	6/6	15/15	1.000
Macropustulation (giant yellow globules)	3/6	3/15	0.2906
Micropustulation (yellow globules)	3/6	5/15	0.631
Scales/Crusts
Islands of brownish plates with double-edged scales	6/6	0/15	<0.001
Silvery-white scales	5/6	13/15	1.000
Pustulation around scales/crusts	4/6	5/15	0.331
Vascular pattern
Dotted vessels	5/6	12/15	1.000
Glomerular vessels	3/6	5/15	0.631
Other findings
Hemorrhagic spots	4/6	8/15	0.659

Although the clinical history and evolution of the skin lesions or arthritis may help in clinical differentiation, the diagnosis may become difficult in ReA patients who present later in their disease course or who have been partially treated. To the best of our knowledge, there has been no report on dermoscopic features of ReA. We documented the dermatoscopic features of ReA, which correlates with the evolution of the lesions and histopathology. The early pustular phase showed homogenous yellow lakes of pus (giant yellow-globules) corresponding to the larger spongiform epidermal neutrophilic collections [Figure 1a]. Older lesions showed islands of brownish plates, which are the result of dried-up macropustules leaving brownish plates in the center which separate at the weaker flaccid walls of pustules giving an appearance of “double-edged scales” [Figure 1b]. This corresponded to parakeratotic debris. Hemorrhagic spots and dotted/glomerular vessels corresponded to dilated dermal capillaries on histology.

Circinate morphology of cutaneous lesions in ReA has been reported.[2] Such a global appearance cannot be appreciated on a 3–4-mm skin biopsy specimen, which may be the reason for the inability to differentiate these entities on histology. Dermoscopic differentials of “double-edged” or “trailing” scales are ichthyosis linearis circumflexa lesions of Netherton's syndrome, erythema annulare centrifugum, and pityriasis rosea.[3]

In summary, we put forward “islands of brownish plates with double-edged scales” as a dermoscopic clue to the diagnosis of ReA. However, a larger comparative study is warranted to validate our findings.

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Conflicts of interest

There are no conflicts of interest.