Phalangeal microgeodic syndrome (PMS) is a rare condition thought to result from a transient disturbance of peripheral circulation under cold temperatures. PMS is most prevalent in children, mainly affecting the fingers and rarely the toes. Although some cases of adult-onset PMS have been reported, the clinical features remain unclear. Herein, I report the case of a 24-year-old man who developed PMS with toe involvement. The self-limiting course was followed by magnetic resonance imaging (MRI). Furthermore, I performed a literature review and summarized the characteristics of this case and eight previously reported adult-onset PMS cases (n=9). The median patient age was approximately 43 (range: 18-89) years, and most cases were diagnosed based on frostbite-like symptoms in winter and specific MRI findings, despite normal radiographic findings. While adult-onset cases had similar clinical and imaging features to child-onset cases, toe involvement was frequent (5/9 [56%]), and female patients were dominant (8/9 [89%]). Two patients had immune-mediated diseases, such as systemic lupus erythematosus and psoriasis. These reports suggest that adults and children with PMS have some different clinical characteristics. Thus, clinicians should consider PMS when finger or toe pain occurs in cold environments, even in adults.

We present the clinical and radiological characteristics of phalangeal microgeodic syndrome in a cluster of five children during the second peak of COVID-19 pandemic in the UK. Each child presented with phalangeal swelling and erythema, prompting a comprehensive multi-disciplinary team review to analyse the clinical presentation, blood test results and imaging. The cohort's average age was 14.1 years, ranging from 10.4 to 16.6 years, with two girls and three boys. Four children experienced phalangeal involvement in the hands, whilst one was affected solely in the feet. A rheumatological work-up was performed for all. Hand X-rays performed on three children revealed distinct radiographic features like microgeodes, subperiosteal bone resorption and rarefaction in two cases. However, further MRI showed extensive changes closely correlated with the clinical signs of cutaneous vasculopathic rashes. The MRI abnormalities were notable, encompassing marrow oedema primarily affecting metaphyses and epiphyses, displaying broad transition zones. Soft tissue swelling and cortical erosions were also observed. These MRI features proved more pathognomonic in the acute clinical context. The study concluded that phalangeal microgeodic syndrome, characterised by digital swelling and erythema, might not be adequately assessed by plain X-rays. The more comprehensive MRI features, including marrow oedema and soft tissue abnormalities, appeared to be more indicative in diagnosing the condition. Considering the rarity of this syndrome and its temporal association with the COVID-19 pandemic, the study hypothesised that COVID-related thrombophilia and immune-mediated vasculopathy might act as crucial triggers for the active bony manifestations seen in this syndrome. KEY POINTS: • PMS is a rare, predominantly paediatric condition, of unknown aetiology which affects the digits. • Laboratory investigations are generally negative; however, in the appropriate clinical context, the X-ray findings of microgeodes and pattern of bone marrow oedema seen on MRI are pathognomonic. • Considering the rarity of PMS and temporal association with the COVID-19 pandemic, COVID vasculopathy may represent a previously unrecognised aetiology for PMS.

Phalangeal microgeodic syndrome (PMS) is a rare osteolytic disorder of unknown etiology that typically affects children up to 15 years old during colder months. Transient peripheral circulatory impairment probably underlines its pathogenesis. Conservative treatment with eviction of cold exposure is often successful. We report the case of a young woman presenting with joint pain in her feet, along with toe discoloration and redness, where a diagnosis of PMS was established based on magnetic resonance imaging findings and exclusion of other differential diagnostic entities. Pharmacological treatment was deemed necessary for symptomatic relief, but a trial of calcium channel blocker (CCB) was not tolerated by the patient. The patient was then started on pentoxifylline, with significant clinical improvement.

Phalangeal microgeodic syndrome (PMS) is a rare rheumatological disease affecting children strongly associated with cold weather. It is considered to be benign and self-limiting, with most cases resolving in warmer months, and no studies have investigated its association to autoantibodies or viral infection. In this peculiar case, a 12-year-old child with the previous COVID-19 infection developed PMS that did not improve in the warm weather and, subsequently, Raynaud's phenomenon and facial rash. With the increasing number of new studies showing the correlation between COVID-19 and autoimmunity, this case report highlights a plausible link between COVID-19, PMS, and autoimmunity in the pediatric population that should be investigated further.