Acral persistent papular mucinosis (APPM) is a chronic, localized subtype of papular mucinosis, also known as lichen myxedematosus (LM). LM is characterized by lichenoid cutaneous manifestations, mucinous deposits, fibroblast proliferation, and dermal fibrosis. APPM is distinct in its localized nature, primarily affecting the extensor surfaces of the distal forearms and hands. Notably, it lacks systemic involvement and is not associated with the thyroid diseases seen in generalized forms [1]. To our knowledge, only six cases have been reported in the United States, with approximately 70 additional cases documented across Europe, North America, South America, and Asia, highlighting the limited available literature [1-5].

Classically, APPM presents as asymptomatic, solitary, white- or flesh-colored papules on the extensor surfaces of the hands, wrists, and dorsal forearms, ranging from 2 to 5 mm in size. These papules contain mucin deposits in the upper reticular dermis and often persist for years [1,6]. Nonetheless, uncommon outliers exist, with APPM-like mucinosis reported on the legs and chest [7-9]. Additionally, pruritic lesions have been reported in isolated cases [2]. These findings challenge the traditional assumption that APPM is an asymptomatic cutaneous condition limited to the forearms and hands. A potential genetic and environmental role has been suggested based on familial occurrences of APPM; however, the etiopathogenesis of the disease has yet to be explored extensively and remains uncertain [2,9].

Herein, we present two cases of APPM, helping to shed light on a condition currently underreported in the medical literature. Consent for the publication of all patient photographs and medical information is provided by the authors, stating that all patients gave consent for their photographs and medical information to be published in print and online versions and with the understanding that this information may be publicly available.

Case 1: A 64-year-old female patient with papular eruption on the hands (Figures 1 and 2).

A 64-year-old female patient with no significant past medical history presented with a several-year history of an intermittently pruritic papular eruption on both hands. Physical examination revealed multiple superficial flesh-colored papules ranging from 2‐5mm in size on the bilateral dorsal hands, wrists, and distal forearms (Figure 1). Biopsy from the left wrist demonstrated focal cutaneous mucinosis, and a colloidal iron stain confirmed mucin deposition within the superficial dermis (Figure 2). Serum protein electrophoresis and urine protein electrophoresis were negative, aiding in ruling out an underlying monoclonal gammopathy. The patient was diagnosed with APPM and elected to defer any treatment. There has been no progression or spontaneous resolution of her condition to date.

Case 2: A 67-year-old male patient with papular eruption on the dorsal hands and wrists (Figure 3).

A 67-year-old male patient with no pertinent past medical history presented with a several-year history of stable papular eruptions on the dorsal hands, wrists, and distal forearms. The physical examination revealed focally scattered, flesh-colored, spongy papules measuring 2‐5 mm in size. A biopsy from the right dorsal wrist revealed focal cutaneous mucinosis. Based on the clinicopathological correlation and lack of systemic involvement, a diagnosis of APPM was made. The patient deferred treatment and was subsequently lost to follow-up; to our knowledge, there was no progression or spontaneous resolution of his condition during the observed period.

We present two additional cases of APPM, adding to the six previously reported cases in the United States literature [2]. This may reflect either a rising recognition of the condition or significant underreporting to date.

Notably, both of our patients were predominantly asymptomatic and had no underlying medical conditions, consistent with prior reports suggesting that APPM is not associated with systemic disease or an underlying gammopathy [10]. Unlike other forms of LM, APPM is a skin-limited condition with a favorable prognosis.

Accurate diagnosis of APPM is crucial to differentiate it from generalized LM, scleromyxedema, which can have organ involvement and may be fatal without proper diagnosis and treatment. Diagnostic features of APPM include the presence of ivory to flesh colored papules ranging 2‐5mm in size, female predominance, persisting without spontaneous resolution, and the absence of systemic disease overlap or associated gammopathy [10]. Histologically, APPM is characterized by focal, well-circumscribed mucin in the papillary and mid dermis, sparing the Grenz zone, with the absence or variations of fibroblast proliferation [10]. Unlike other forms of LM, including discrete papular mucinosis, which may resolve spontaneously, APPM generally persists over time, as observed in our cases [2].

A variety of treatment strategies for APPM have been described in the literature. Topical and intralesional corticosteroids have shown minimal to no clinical improvement [2]. Tacrolimus 0.1% ointment has been postulated as a potential treatment option for LM by inhibiting tumor necrosis factor (TNF)-α secretion and transforming growth factor (TGF)-β-induced collagen synthesis, although only a partial response has been reported in the literature [2,9]. Destructive modalities, such as electrofulguration, have demonstrated efficacy in lesion resolution, albeit with mild scarring [2].

In conclusion, our case series highlights the importance of recognizing APPM and adds to the 70 documented cases worldwide, including now eight from the United States (Table 1). As APPM remains an underreported entity in the medical literature, these cases serve to enhance awareness and encourage further exploration into its clinical variability, etiology, genetic predispositions, and optimal management strategies. Importantly, our cases provide additional evidence to support accurate diagnostic approaches that help distinguish APPM from more severe forms of LM, such as scleromyxedema. Proper diagnosis can help prevent unnecessary treatment and testing. Increased recognition of APPM will ultimately enhance understanding of the condition and guide better management, leading to improved outcomes for affected patients.