Acrodermatitis Continua of Hallopeau: A Diagnostic Challenge

Introduction

Acrodermatitis continua of Hallopeau (ACH), a rare condition, is a sterile pustular eruption of one or more digits and has a chronic clinical course. It is also known as acrodermatitis continua suppurativa, acrodermatitis perstans, dermatitis perstans, acropustulosis, and dermatitis repens.[1–3] The classical presentation is tender, sterile pustules with underlying erythema appearing on the tip of a digit, more commonly on a finger than a toe.[4] The eruption is most typically associated with local trauma or infection; however, this is not always the case, and neurological and inflammatory etiologies have also been reported.[4,5] If the nail apparatus is not involved, then other diagnoses such as palmoplantar pustulosis (PPP) should be examined.[6] ACH develops into a chronic condition that might proceed proximally to the dorsal portion of the hand or foot. Without therapy, ACH can progress to a variety of problems, including onychodystrophy, which can cause anonychia, and osteitis, which can cause distal phalange osteolysis.[7] In these ways, ACH can induce severe impairment and have a significant negative influence on patients’ quality of life.

In terms of classification, ACH is classified as a localized pustular psoriasis.[8] It appears to be most common in middle-aged females, but because ACH is so uncommon, epidemiological data is restricted to case reports.[9] In addition, there are no defined criteria for treating ACH; instead, case reports with a variety of therapeutic techniques and outcomes are available.

ACH is linked to a range of genetic alterations in the genes IL36RN, CARD14, and AP1S3, according to current data. Generalized pustular psoriasis (GPP) and PPP, two phenotypically related pustular skin diseases, are linked to mutations in these same genes.

Clinical features

Typically symptoms of ACH begin with the tip of one digit turning erythematous and subsequently developing tender pustules that migrate under the nail bed and matrix, finally leading to onychodystrophy. Traditionally described, the pustules rupture and cluster in the acute phase, forming “a lake of pus that carries the nail away.” The resulting anonychia leaves behind a shiny, erythematous, and smooth distal digit where pustules frequently regenerate.[10] The affected digits might become hyperkeratotic with psoriasiform scaling and pustulation as the disease develops. ACH can proceed to affect other digits or extend proximally to the dorsal hand or foot in long-term instances; however, the disease usually remains confined to the digit(s) for months or years before progressing this far. The classic findings of ACH are shown in [Figures 1 and 2]. In severe cases, the condition can induce osteitis of the underlying phalanges, which can lead to osteolysis. The histopathology of ACH is essentially psoriatic, but the central feature is a fully developed, large pustule within the epidermis, unilocular and full of neutrophils with some overlying parakeratosis. At times large numbers of mast cells and eosinophils may be present predominantly around the acrosyringium.

Figure 1.

24-year-old female patient presented with pustules, scaling, erythema, and nail dystrophy of all digits except left-hand index finger which were consistent with chronic ACH

Figure 2.

Dystrophy of all the fingernails except the left index finger showing involvement of nail folds and the pulp of digits

Differential diagnosis

ACH is often misdiagnosed due to its pus-filled lesions which may mimic bacterial, fungal or viral paronychia. Secondarily infected contact dermatitis, dyshidrotic eczema, or a paraneoplastic disease are all differentials, depending on the patient’s age and comorbidities. Other infections of the digits, such as herpetic whitlow, can cause vesiculopustules, while dermatophytosis can cause scaly erythema, both of which are similar to ACH. Autoimmune bullous disorders, such as pemphigus vulgaris, can mimic ACH by causing digit erosion and inflammation. Squamous cell carcinoma, glomus tumor, pyogenic granuloma, melanoma, Reiter’s disease, subungual fibroma, blastomycosis, and onychomycosis are all differentials that might cause late clinical signs of ACH.

PPP, however, needs to be compared and differentiated from ACH. Several key features distinguish these two separate entities. Firstly, PPP rarely involves a history of injury, whereas ACH frequently follows trauma. Secondly, ACH has suppurative nail involvement early on, whereas PPP does not necessarily impact the nails and is usually non-suppurative. Thirdly, ACH is usually unilateral, confined to a small number of fingers, and has an inconsistent distribution over several years, whereas PPP is usually bilateral and symmetrical. Finally, symptoms observed in ACH, such as soft tissue sclerosis and osteolysis, are not found in PPP.

However, there are various clinical features of ACH that support its classification as a pustular psoriasis variant. Firstly, genetic mutations common to patients with ACH, PPP, and GPP suggest these conditions are on the same auto-immune inflammatory spectrum. Secondly, arthritis and joint pain is common in both ACH and PPP with features of psoriatic arthritis in radiology. Also, the presence of a geographic tongue is seen in ACH and other auto-immune inflammatory conditions like PPP. Lastly, ACH can progress to life-threatening von Zumbusch type of GPP.[11] Such complications should be diagnosed early and managed aggressively. The differential diagnoses and the differentiating features are summarized in Table 1.

Table 1.

Differentiating points of ACH comparing the other differential diagnoses

Differential diagnosis	Differentiating features from ACH
PPP	Rarely there is a history of trauma, whereas ACH often follows trauma. PPP is mostly bilateral and symmetrical. PPP does not always affect the nails and is usually non-suppurative. Osteolysis and soft tissue sclerosis are absent.
Bacterial infection: Paronychia	Acute onset, rarely recurrent, painful, pus discharge, and response to antibiotics.
Onychomycosis and candidial paronychia	Indolent chronic course, positive potassium hydroxide mount, and response to antifungals.
Viral paronychia	Acute onset, painful, and presence of vesicles.
Secondarily infected contact dermatitis	Initial presentation of itchy papular or vesicular rash, followed by pustules and inflammation. Response with topical steroids and antibiotics. The course is not chronic or recurrent.
Paraneoplastic process	Presence of an underlying malignancy and responds if the underlying primary is treated.
Pemphigus vulgaris	Presence of oral mucosal lesions and associated flaccid bullae and erosions over the body. Nails are never affected in isolation.
Squamous cell carcinoma	Multiple nails are not affected. The disease course is not relapsing and remitting but progressive. The morphology is different.
Melanoma	Only one nail is affected and positive pigmentary changes including Hutchinson’s sign.
Pyogenic granuloma	Progressive chronic history of bleeding on touch and the affection of the nail folds and mostly nail plate and bed is intact.
Reiter’s disease	Systemic involvement and nails are not the only affected part. Morphology of the presentation is also different.
Glomus tumor	Nail bed affected in one or two nails and tender isolated nodules are present.

Treatment

ACH is characterized by its refractory and chronic nature, and spontaneous improvement is uncommon. Treatment options are mostly mentioned in anecdotal case reports and randomized studies are not there due to the rarity of the condition. Traditionally, the most popular treatments for ACH were identical to those for other types of psoriasis, particularly PPP, including topical and oral corticosteroids, topical and systemic retinoids, topical calcineurin inhibitors, topical vitamin D analogs, topical tar and fluorouracil, cyclosporine, methotrexate, and phototherapy or photochemotherapy.[2] A combination of systemic and topical medicine is the most preferred option. Off late, biologics like anti-tumor necrosis factor agents infliximab, adalimumab, etanercept, and interleukin-17 (IL-17) inhibitors like secukinumab have given sustained and rapid response.

Recent advances

In addition, the discovery of IL36RN mutations as a genetic factor to ACH has aided the development of biologics that block IL-36 signaling specifically.

The use of existing and developing biologic medicines to treat ACH, particularly those that are resistant to standard therapies, is a research and development area that is still being explored. Although no one treatment has been identified as superior for ACH, numerous have shown efficacy, signaling a promising new chapter in the management of this chronic and often debilitating condition.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.