Acroosteolysis (AO) is a rare condition characterized by resorption of the distal phalanges of the fingers and/or toes. It can be familial, idiopathic (IAO), occupational, or secondary. Other authors suggest a classification into primary (genetic disorders, lysosomal storage disorders) or secondary AO. Various skin and nail changes have been reported in this condition. However, the cutaneous change on the affected digit(s)/toe(s) during the natural course of AO has been poorly documented. A 5-year-old girl presented with a 3-month history of a distinct transverse boundary between normal skin proximally and affected crusted skin overlying osteolysis distally (“split” sign) on the plantar surface of the third toe. This boundary gradually elongated circumferentially to involve the dorsal surface. The mother gave a similar history of a delimitation line on the 2nd, 4th, and 5th toes of the right foot with durations of 3 months, 1 year, and 2 years, respectively, that disappeared before she noticed a shortening of those toes. X-rays revealed partial resorption of the terminal phalanx of the third toe and several lytic changes in the middle and terminal phalanx of the second, fourth, and fifth toes. The clinical features, radiology findings, and a workup that helped rule out conditions associated with AO (secondary AO) helped establish the diagnosis of IAO in our patient. This case study highlights that the natural course of IAO includes distinct skin findings, such as the “split” sign that we describe. This sign can help identify the condition early.

© 2023 The Author(s). Published by S. Karger AG, Basel

Acroosteolysis (AO) is characterized by destructive lytic changes in the distal phalanges [1]. Radiologically, it can be transverse (band) osteolysis of the shaft of the distal phalanx or longitudinal osteolysis of the distal end of the phalanx, which is the most common type [2]. Based on the etiology, AO can be familial, idiopathic (IAO), occupational (secondary to exposure to vinyl chloride), or secondary [3]. Other authors suggest a classification into primary (genetic disorders, lysosomal storage disorders) or secondary AO [4]. It can be seen in various genetic disorders [5, 6]. Various skin and nail changes have been reported in this condition. However, the cutaneous change on the affected digit(s)/toe(s) during the natural course of AO has been poorly documented. Here, we present a girl with AO and highlight the course of the condition with a focus on a distinctive skin sign.

A 5-year-old girl born to noncontagious parents, after an uneventful pregnancy, developed a transverse cutaneous “split” on the plantar aspect of the right third toe for 3 months that was associated with serous discharge. Gradually, the “split” elongated circumferentially over a period of 1 month to involve the dorsal aspect of the toe. The mother gave a similar history of a demarcation line on the second, fourth, and fifth toes of the right foot with durations of 3 months, 1 year, and 2 years, respectively, that disappeared before she noticed a shortening of those toes. The patient had no history of traveling, Raynaud phenomenon, trauma, exposure to vinyl chloride gas, skin fragility, blisters at the site of trauma, joint pain, or swelling of the extremities. Her family members did not have similar lesions. The examination did not detect palmoplantar keratoderma, manifestations of connective tissue disease, hirsutism, or dental or musculoskeletal abnormalities.

Examination of the feet revealed a distinct boundary between normal skin and affected crusted skin overlying osteolysis (“split” sign) on the third toe involving circumferentially the entire toe (Fig. 1). It was slightly painful and associated with serous discharge but no discharge of the bony spicules. Additionally, there was a shortening of the distal phalanx of the second, fourth, and fifth toes. The sensation and peripheral pulses of the feet were normal. X-rays of the right foot revealed complete resorption of the middle and terminal phalanx of the fifth toe, complete resorption of the terminal phalanx of the fourth toe, partial resorption of the terminal phalanx of the third toe, and partial resorption of the middle and terminal phalanx of the second toe (Fig. 2).

Right foot: a circumferential, distinct boundary (“split”) between normal and affected, crusted skin overlying osteolysis (red arrow), and shortening of the 2nd, 4th, and 5th toes.

Anteroposterior (right) and oblique (left) X-ray views of the right foot show complete resorption of the middle and terminal phalanges of the 5th toe, complete resorption of the terminal phalanx of the 4th toe, partial resorption of the terminal phalanx of the 3rd toe, and partial resorption of the middle and terminal phalanges of the 2nd toe.

Consultations with several specialists ruled out cardiac, respiratory, ophthalmologic, and otologic problems. Laboratory investigations that included complete blood count, renal function tests, liver function tests, parathyroid hormone, anti-nuclear antibody, rheumatoid factor, anti-CCP test, C-reactive protein, fasting blood sugar, serum calcium, inorganic phosphate, albumin, and thyroid function tests were in normal ranges. This workup helped rule out infections, e.g., osteomyelitis, connective tissue, endocrine, and lipid storage disease. There were no clinical or radiographic findings of inflammatory/rheumatic disorders such as psoriatic arthritis. The clinical and radiologic features and workup helped establish the diagnosis of IAO in our patient.

AO is a rare condition characterized by resorption of the distal phalanges of the fingers and/or toes that may be transverse or longitudinal radiologically [1]. It can be seen in various genetic disorders such as Haim-Munk and Hajdu-Cheney syndromes and lysosomal storage disorders [5, 6]. IAO typically begins in early childhood, adolescence, or early adulthood and progresses through life, although we have report of its onset in mature adulthood. It is an extremely rare condition with only very few cases reported in the English literature [1, 3, 7–10]. Several cases of IAO of the hands have been associated with progressive osteolysis of the mandibular ramus and multiple cortical defects [9, 10].

Secondary AO, in classifications where genetic disorders are not included, typically begins in early adulthood and has several etiologies, including vasculopathy such as Raynaud syndrome; inflammatory disorders such as rheumatoid arthritis, psoriatic arthritis, and systemic sclerosis; infection; metabolic disorders; and trauma [2, 4]. In our case, there was no family history of the condition, and the laboratory and clinical investigations ruled out secondary causes. Haim-Munk syndrome, which manifests with AO, was ruled out by the absence of palmoplantar keratoderma, severe early-onset periodontitis, onychogryphosis, pes planus, and arachnodactyly [5]. Hajdu-Cheney syndrome, also characterized by AO, was ruled out by the absence of osteoporosis and craniofacial and other musculoskeletal anomalies such as elongated fibulae [6].

Various skin manifestations have been documented in AO. Familial AO affects only the feet and is associated with plantar ulcerations [11]. Cutaneous findings in AO associated with primary hypertrophic osteoarthropathy include palmoplantar hyperhidrosis, skin thickening, and forehead and scalp furrowing. AO secondary to exposure to vinyl chloride is associated with papules and nodules on the hands and forearms, thickening of the skin of the hands (sclerodermatous change), puffiness of the face, and Raynaud phenomenon [3]. Papular mucinosis associated with AO has been reported in scleroderma [12]. Nail changes in AO include brachyonychia/racket nails, anonychia, atrophy, transverse ridges, discoloration, thickening of the nail plate, hyperkeratosis of the cuticles, pincer nail, pitted onycholysis, longitudinal ridging, and pterygium [4].

Knowledge of cutaneous changes during the course of AO can assist in the early recognition and prevention of disease progression. The disease may be misdiagnosed until a clear deformity is developed. Giaccai described the clinical features of “familial and sporadic neurogenic acro-osteolysis” in the 1950s and reported “chronic ulcers of the extremities associated with changes in the underlying bone structures” [13]. The familial type of neurogenic AO begins in childhood or early adolescence as swelling or blister on the sole that ruptures, resulting in a mildly painful ulcer. After a few weeks or months, the ulcer grows and becomes deeper with discharge of the bony spicules. Subsequently, the ulcer may heal spontaneously. This process repeats itself after weeks or months until the development of a deformity. Familial AO is associated with bilateral sensory loss that extends proximally.

IAO affects hands more than feet. Unlike the familial form, IAO does not show neurologic abnormalities and rarely ulcer formation [8]. Two cases of IAO showed discrete yellow papules on the upper extremities [3, 14]. IAO may be associated with Raynaud’s phenomenon [13, 15]. In our case, the natural course of the condition, characterized by a distinct cutaneous boundary with later partial resorption of the terminal phalanx, was different from previously reported. The CARE Checklist for this case report has been completed by the authors and is attached as online supplementary material (for all online suppl. material, see www.karger.com/doi/10.1159/000529727).

This case study highlights that the natural course of IAO includes skin findings such as the distinct cutaneous boundary (“split” sign) on the affected toe we describe. This skin sign can help detect resorption of the phalanx promptly and should be recognized by the clinician.

This retrospective review of patient data did not require ethical approval in accordance with local/national guidelines. A written informed consent was obtained from the parents for publication of this case report and any accompanying images. We are thankful that they provided a detailed history.

The authors declare that they have no competing interests.

This study received no funding.

Samir Shrestha and Raksha Pathak were involved in the direct management of the patient. Bashant Regmi was involved in the radiology assessment of the case. Samir Shrestha and George Kroumpouzos drafted the first manuscript and reviewed the literature. George Kroumpouzos supervised the manuscript drafting. All authors read and approved the final manuscript.

All data generated or analyzed during this study are included in this article online supplementary material files. Further inquiries can be directed to the corresponding author.

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