Introduction

Dermatologists have seen their fair share of skin infections, dermatitis, acne, to mention but a few, but what if some skin conditions look similar to each other? How would they know the difference? For Lichen nitidus (LN), we will explore how to recognise this skin condition and the signs dermatologists would point out, distinguishing it from other similar skin conditions.

LN appears as pearly, small, and discrete papules that are uncommon but usually harmless. Even if it exhibits an inflamed nature, it is often asymptomatic and is frequently mistaken for other conditions, such as keratosis pilaris, psoriasis or flat warts.^1,2

To assist clinicians in recognising the key characteristics of LN, they would need to accurately diagnose the condition to prevent any unnecessary treatments and investigations. They would look out for shiny, pink lesions in groups and possibly hyperpigmented if you have darker skin.¹

LN tends to mimic other disorders, making it difficult for clinicians to spot it straight away. Clinical awareness is crucial, so this article serves as a practical guide for identifying LN, supporting dermatologists, providing microscopic hints, and offering tips for managing recurring cases carefully.¹

What is lichen nitidus?

LN is a chronic inflammatory dermatosis with an unknown cause. The presence of this skin disorder is shown as distinct, tiny papules. It commonly appears on the limbs, abdomen, chest, and male genitalia but can form anywhere.^1,3 These skin-coloured bumps generally affect children and young adults, though they can occur at any age. The condition begins insidiously and could be overlooked, especially when producing no symptoms. Patients are usually unaware of this condition until noticed during a routine examination.¹ 

The condition differs from person to person. It can either go away on its own, without any treatment, or stay for years and remain stable and mild. LN is unpredictable. In rare cases, LN can appear all over the body. Some associated conditions that often coexist with LN include lichen planus, atopic dermatitis and vitiligo, as they share the same mechanism. ⁴

LN is often undiagnosed due to its mild nature. It affects all genders and races equally. There are no specific environmental factors, lifestyles, or inherited traits linked to the condition. There have been cases of families with the condition, but no solid proof. LN does not require treatment unless a dermatologist says otherwise. The only medical complications that could occur are itchiness and swelling due to irritation. Some people worry about the appearance, but fortunately, it does not cause any long-term scarring. LN cannot be avoided, does not affect daily life, and is not contagious. ³

Clinical presentation and morphology

The appearance of LN is recognised by its familiar, skin-coloured papular bumps. The size and shape are about 1-2 mm wide and can be seen as flat or slightly rounded on the skin's surface. The description of these lesions is shiny or pearly looking under direct light, and they feel smooth. It can scatter across the skin, but in other cases, it can merge into small patches in places where there is friction or skin folds, such as the groin area, wrists, and elbows.^3,4

The trunk and abdomen are most commonly affected. The least frequent are the palms of your hands, the soles of your feet, and the mucous membrane. The mucous membrane is the genital lining, and LN can only be diagnosed if examined carefully by a healthcare professional.³

Most cases show no symptoms, but some patients have reported some mild itchiness. This could happen if environmental factors affect your body. As the temperature rises, you would sweat and cause friction due to stickiness. This can worsen the lesions because of irritation. The condition does not cause any pain or any other symptoms.³

LN does not always look the same and can appear differently depending on where it is on your body and how it shows up. When the skin experiences minor trauma, like any pressure from scratching or rubbing, some papules can appear along the line where it has been injured. This is called the Koebner phenomenon. The associated name is linear LN.^1,2

Another variant called generalised LN involves lesions in larger areas of the body. This is commonly seen in children. The large areas of their body, mostly in their chest, back, and arms, will show LN a bit more dramatically. It is still harmless.¹ 

There is a rare case of LN, named the palmoplantar variant, which causes the papules to thicken around the palm or sole area. These areas will feel harder and thicker. It looks similar to eczema or keratosis pilaris, and because of this resemblance, it is difficult to diagnose accurately, even with a trained eye. To distinguish LN from other conditions, it is important to recognise certain patterns that set them apart.¹

Histopathology and diagnostic features 

Clinical appearances will not give a definitive answer. Dermatologists or other healthcare professionals can perform a skin biopsy to get an accurate diagnosis of LN. A histopathological examination involves studying tissue samples under a microscope. Performing this examination can identify a certain characteristic pattern called a “ball-and-claw” configuration.¹ The “ball” refers to a well-defined lymphohistiocytic infiltrate within the dermal papillae and surrounded by the epidermis, almost “claw-like” due to the lengthened ridges it shows under a microscope.^1,4 

Another feature that is noticeable under a microscope to confirm the diagnosis is parakeratosis. This means the nuclei are still present in the outer layer of the skin, where they shouldn’t normally be. This is because the skin cells are not maturing properly, which is a sign of LN.^1,5

Another extra detail of LN is vacuolar degeneration of the skin's basal layer. The basal layer is the deepest part of the outer layer, and when vacuolar degeneration occurs, the cells under the microscope look damaged and have small clear spaces. That is a sign of inflammation, as the immune cell activity increases and the blood vessels dilate in the upper layer to give it the redness in LN.^1,6

Now we compare how to support the diagnosis of LN. Differentiating histological findings will help contrast LN from other conditions. Lichen planus is also an inflammatory condition, but the appearance is more saw-tooth shaped, which claws around a clump of immune cells that spreads wider on the base layer.⁷ With flat warts, it does not show the ball-and-claw pattern under a microscope and is caused by HPV. The microscopic differences can tell them apart.⁸

A skin biopsy is useful when a rash or a cluster of bumps looks unusual and covers a larger area than normal. It is important to consider other conditions to make an accurate diagnosis and avoid improper treatment.

Dermoscopy and imaging clues

Dermoscopy is a non-invasive tool that can aid in the physical exam of LN. One characteristic feature that specialists look out for under a dermoscope is a central white area within the linear vessels. Under the polarised light, shiny, white lines appear. Clinicians point them out as chrysalis, which are surrounded by the weak visibility of erythema or the linear vessels. These reflect underlying dermal fibrosis and altered collagen.^9,10

These dermoscopy features for LN help in recognising other conditions such as molluscum contagiosum, which has the same appearance as the pearly papules but is an infection caused by a virus.¹¹ As stated before, flat warts have a rough surface and scattered vessels, but no shiny aspects.⁸ Lastly, Lichen planus has painless white streaks, which are not seen in LN.⁷

Visual assessments that doctors use to help improve the identification of LN can be made by using imaging tools. 

• Dermoscopy can magnify skin structures and reveal patterns, colours, and vascular features that cannot be seen by the naked eye
• High-resolution photography is useful for discovering any subtle changes in shape
• Reflectance confocal microscopy (RCM) is a new non-invasive technique which provides real-time microscopic imaging to support diagnosis¹²

Differential diagnosis

Here are some other key conditions that can mimic LN:

Lichen planus

• Similarities: Small papules on the skin
• Differences: It gives off a purplish hue, the shape is more polygonal than round, it can cause itching, and it has the saw-tooth ridges that are widespread⁷

Molluscum contagiosum 

• central umbilication, viral cause
• Similarities: skin-coloured papules that have a dome-like shape
• Differences: caused by a poxvirus, in dermoscopy, it has a central pore a small dimple in the middle of a skin lesion¹¹

Flat warts

• Similarities: they have flat tops on the bumps
• Differences: rougher surface, larger than LN, more common on the backs of hands and on the face, and has a history of viral features such as koilocytosis⁸

Granuloma annulare

• Similarities: can form in groups
• Differences: appears as a ring shape, is involved in the deeper parts of the dermis, and has mucin in the dermis¹³

Folliculitis

• Similarities: papules appear on the limbs.
• Differences: associated with redness, scaling, inflammation, or pustules, and may follow the hair follicles to create a pattern¹⁴

How to differentiate each:

• Lesion colour: LN is skin-coloured, It does not appear red, purplish, or abnormally thick
• Distribution: most likely on the limbs or genitalia
• Presence/absence of itchiness: a mild or non-existent case in LN
• Dermoscopy: shiny, pearly papules in linear vessels
• Histology: the typical ball-and-claw pattern under a microscope

Management and prognosis

LN often requires no treatment if it is asymptomatic. However, for bothersome or persistent cases where lesions cause distress, targeted therapies can be implemented. 

Treatments involve:

• Topical corticosteroids that can reduce inflammation and improve appearance^1,15
• Calcineurin inhibitors are used for patients who do not respond to steroids; an example would be tacrolimus, which comes with less of a risk for skin thinning^1,16
• Phototherapy, especially a narrowband ultraviolet B (NB-UVB), can be used if there is widespread presentation of LN. If patients wish to avoid long-term topical medication, they often choose this one^1,17

It is important to reassure yourself that this condition does not leave any scars, is gentle, and can resolve itself over time. You should refer to a dermatologist if you are uncertain of the diagnosis, if the treatment is refractory or if other conditions arise along with LN.

Summary 

Although LN directly affects the skin, it is not at all contagious. Despite the similarities which LN and lichen planus both have on the skin, lichen nitidus is incapable of developing into lichen planus. 

When infected with LN, the symptoms tend to last anywhere between a few months to a year.

In some cases of LN, immediate diagnosis may be unclear; therefore, biopsies should be conducted on all cases of lichen nitidus to confirm the diagnosis.