Dermoscopy aiding the diagnosis of acrodermatitis continua of hallopeau

Pustular psoriasis is a distinct subtype of psoriasis with unique etio-pathogenesis, clinical features, course, complications, management strategies [1]. Pustular psoriasis is broadly classified into generalized, localized variants; acrodermatitis continua of Hallopeau ACH is a variant of the latter [2]. We present a rare case of ACH with uncommon clinical presentation. A-56-year-old female with no known co-morbidities presented with painful crumbling of nail plate of the left great toe for 16 months duration. It was insidious in onset and progressive in nature. There was no history of preceding trauma. The crumbling of the nail plate was associated with pain and intermittent scanty non-foul-smelling yellowish discharge. She consulted at various hospitals and was treated with repeated courses of oral as well as topical antifungals and antibiotics with no response. Dermatological examination revealed total dystrophy of the nail plate of left great toe. The nail plate was replaced by thick yellow plate like overlapping scales which when removed revealed moist yellow floor. (Fig. 1) The nail as well as the surrounding area was tender with mild halo of erythema all around the nail. There was no loco-regional lymphadenopathy. Dermoscopy of the nail showed thick yellow overlapping scales with no additional findings. (Fig. 2a) The following differential diagnoses were considered pustular psoriasis of nail/ACH, onychomycosis with secondary bacterial infection, tuberculosis of the nail bed, subcutaneous mycosis and squamous cell carcinoma of the nail bed. A bedside 10% KOH mount from the scarping of the nail bed did not show any hyphae or spores. The extracted scale as well swab from the wound bed was sent for bacterial, mycobacterial and fungal staining and culture in which Pseudomonas was isolated, however mycobacterial and fungal culture showed no growth. Polymerase chain reaction on swabs for M. tuberculosis was negative, so was interferon gamma release assay and Mantoux test. Radiography and MRI of the left great toe nail did ruled-out any underlying bony or soft tissue involvement. Nail bed biopsy revealed anucleate sheets of squamous overlying fragmented stratified squamous epithelium. The dermis showed areas of necrotic infiltration of neutrophils suggestive of Munro’s micro-abscesses. (Fig. 2b). There were no granulomas, histiocytic collections or evidence of malignancy. She was diagnosed as a case of pustular psoriasis of the nail/ACH and was started on twice daily application of 0.05% lotion halobetasol. The pain and discharge reduced after a week finally resulting in complete clearance of pustular lesions and scales in a month, revealing underlying healthy nail bed. (Fig. 3)Figure 1: Left great toe nail plate completely destroyed by disease. The nail bed is covered with yellow to white scales. The crust removed from proximal part of nail bed shows erosion covered with purulent exudate. There is erythema on the proximal as well as lateral nail folds.Figure 2: (a): Polarized light Dermoscopy examination (x10) reveals thick yellowish white overlapping scales completely covering the nail bed. (b): Nail bed biopsy shows anucleate sheets of squames overlying fragmented stratified squamous epithelium. The dermis shows areas of necrotic infiltration of neutrophils suggestive of Munro’s micro-abscesses.(H and E, ×40)Figure 3: Complete clearance of scales as well as pustular lesions revealing healthy nail bed after four weeks of application of topical steroids.ACH typically affects the subungual/distal area of one or several fingers and/or toes as multiple sterile pustules on an erythematous base associated with scaling/hyperkeratosis [3]. It is often misdiagnosed as onychomycosis especially when affecting a single digit as seen in our case [4]. Dermoscopy is a simple tool which has been proven to distinguish ACH from other differential diagnoses. Dermoscopy of ACH shows yellowish white hyperkeratosis/scaling along with single or multiple pustules [5]. In addition, dotted and linear vessels may be seen. The diagnosis of ACH in our case was confirmed by histopathology. Our patient was successfully treated with topical steroids achieving complete clearance of scales and pustular lesions revealing healthy nail bed underneath in four weeks. Hence, dermoscopy is a valuable tool to diagnose ACH. The diagnosis of ACH in our case was confirmed by histopathology using dermoscopy as a handy screening tool. Acknowledgements We sincerely thank the patient who allowed us to share his information by providing consent. Funding: This case report received no external funding. Declaration of patient consent: The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. Conflicts of interest The authors declare no conflict of interest.