Keratoderma Blenorrhagicum - An Overview

Introduction

It is the characteristic cutaneous manifestation of reactive arthritis, occurring in only ten percent of the affected population. It usually appears one to two months after the onset of arthritis but may accompany or rarely precede the initial manifestations.

The soles of the feet are almost always involved, but the extensor surfaces of the legs and the dorsal aspects of the toes, feet, hands, fingers, nails, and scalp are common sites. The initial lesion is a dull red macule rapidly becoming papular and pseudo-vesicular. It eventually erupts and transforms into a harder and elevated plaque; if the eruption is widespread, it may evolve into generalized exfoliative dermatitis (erythroderma).

The clinical and histopathological features of keratoderma blenorrhagicum KB resemble those of idiopathic psoriasis (immune-mediated skin disorder). This is due to KB being an instigating factor for psoriasis; however, the overall pattern, course, and distribution of the lesions in KB are usually distinctive.

What Is Reactive Arthritis (RA)?

• Formerly known as Reiter’s syndrome, it is a triad of nongonococcal urethritis, ocular inflammation, and arthritis. Mucocutaneous lesions (like KB) are sometimes included as a fourth feature.

• This syndrome occurs in one to three percent of patients with sexually acquired nongonococcal infections (most common is chlamydia) of the genital tract. It is also seen in certain gut infections caused by Shigella flexneri, Salmonella enterica, and Campylobacter jejuni.

• The mechanism by which the infection-causing organisms lead to RA (and, in turn, KB) is unclear. One hypothesis is cross-reactivity, in which the antibodies developed against the inciting infection also have an affinity for HLA (human leukocyte antigen)-B27; another hypothesis included cytokines.

• HLA-B27 is a specific protein that causes the body’s immune system to attack healthy white blood cells leading to autoimmune conditions like RA. It is present in a few individuals with a genetic predisposition.

• For an HLA-B27 to cause RA, the individual should have been exposed to a prior infection (either urogenital or gastrointestinal). RA starts within four weeks after infection. The patient experience generalized symptoms like fever, fatigue, and specific urinogenital (urethritis), rheumatological (arthritis), ophthalmological (ocular inflammation), and dermatological (KB) manifestations.

Are There Additional Dermatological Symptoms of RA Other Than KB?

The extra-articular mucocutaneous symptoms of RA other than KB are-

1. Mucosal Ulcers - These start as erythematous macules in the oral and pharyngeal mucosa, which eventually erode and bleed, leading to ulceration.

2. Erythema Nodosum - It is an acute nodular septal panniculitis (inflammation of the fat under the skin) that causes firm, deep, and erythematous nodules on the extensor surface of the legs. The nodules are often painful on palpation.

3. Onycholysis - It is a condition where the nail separates from the nail bed, and a gap develops under the nail. When it starts, there is a white or yellowish patch at the tip of the nail, and then this extends down the cuticle.The gap between the nail and the nail bed can get colonized with bacteria, such as Pseudomonas, producing a dark green pigment. The nail can then become infected and discolored and can be easily mistaken for melanoma.

4. Subungual Keratosis - A condition where a chalky substance accumulates under the nail. The nail becomes raised and tender, especially when the nail's surface is pressed. It can be uncomfortable to wear shoes because the nail may be under constant pressure.

5. Geographic Tongue - It is a condition characterized by the inflammation of the tongue and appears in a map-like (geographic) pattern.

6. Circinate Balanitis - These are the same papulosquamous, psoriasiform lesions seen in KB, except for the location. KB has lesions on the sole and palm, whereas lesions in circinate balanitis are on the glans penis.

How Is KB Diagnosed?

It is based on past medical history and clinical and laboratory findings.

1. Past Medical History - The patient will always have a history of recent or old (most probably genitourinary) infection that they have been treated with the respective medication. The patient will also complain of symptoms of RA (like arthritis) after four weeks of infection due to impaired cellular immunity.

2. Clinical Findings - Physical examination will reveal erythematous skin lesions, confluent, hyperkeratotic, and pseudo bumps on the palms, soles, fingers, and toes. These lesions present as diffuse yellowish hyperkeratotic plaques on the soles.

Other non-dermatological findings of RA that are suggestive of KB are:

1. Genital ulcers and urethritis (inflammation of the urethra).

2. Cervicitis (inflammation of the cervix) in females, and diarrhea.

3. Iritis (inflammation of the iris) and conjunctivitis (inflammation of the conjunctiva).

4. Oligoarthritis (arthritis of four or fewer joints during the first six months of the disease.)

5. Heel pain and fingers shaped like sausages.

6. Laboratory findings include a CBC (complete blood count) test that will reveal leukocytosis, elevated ESR (erythrocyte sedimentation rate), CRP (C-reactive protein), and positive antibodies for the inciting infection. Urinalysis will reveal a positive HLA-B27 test.

Histopathological examination of the skin biopsy will show psoriasiform changes, hyper and parakeratosis, acanthosis, elongation of the rete ridges in the epidermis, and mixed inflammatory infiltrate in the upper epidermis.

Most dermatological features mentioned above are also seen in conditions like pustular psoriasis (a subtype of psoriasis that is characterized by pustules along with the discolored skin), erythema multiforme (a hypersensitivity reaction with characteristic lesions), and hyperkeratotic eczema (eczema comprising of thick scaling of the palms). These can be differentiated from KB with the help of a positive HLA-B27 test and the classical triad of RA.

How Is KB Treated?

Treating KB involves addressing the underlying autoimmune conditions like RA and the previous infection that triggered RA. Acknowledging the dermatological feature of KB facilitates diagnosis and management.

Antibiotics and non-steroidal inflammatory drugs (NSAIDs) should be considered in cases of active infection. The choice of antibiotics depends on the inciting infection, which should be given for at least three months to completely resolve the symptoms (of both RA and KB).

Additional treatment for KB includes systemic corticosteroids and local keratolytic agents (like salicylic acid, lactic acid, glycolic acid, etc.) along with emollients (moisturizing agents applied to the skin directly for hydrating it).

Conclusion:

KB is the mucocutaneous symptom of an underlying condition called reactive arthritis (RA), which is an autoimmune reaction to an infection in patients with positive HLA-B27. Care should be taken while diagnosing the condition, which often mimics other autoimmune diseases. The outcome is excellent when treated with antibiotics, non-steroidal inflammatory drugs NSAIDs, and keratolytic.