Rare case of adult-onset phalangeal microgeodic syndrome of the feet

Abstract

Phalangeal microgeodic syndrome (PMS) is a rare condition typically affecting children and is characterised by painful digits precipitated by cold temperatures. In medical literature, cases appear to be clustered in Japan. Adult-onset PMS is particularly rare and although imaging features are characteristic, it may go undiagnosed, as it is not commonly encountered. We present, to our knowledge, the fifth reported case in the literature of adult PMS, the second to affect the feet rather than hands, and the first in a Caucasian adult patient. This case report aims to raise awareness of this likely underdiagnosed condition to allow optimal management and avoidance of unnecessary diagnostic procedures.

Background

Phalangeal microgeodic syndrome (PMS) is a rare, self-limiting condition that was first described in 1970 by Maroteux.^1–3 Sporadic case reports describe PMS in young children predominantly affecting the hands in cold climates, with only four previously reported adult cases. The underlying pathophysiology is thought to be due to impairment of the peripheral circulation causing a process of transient oedema and subsequent necrosis and connective tissue proliferation.^4–6

Imaging features of PMS are now felt to be pathognomonic with plain radiographs demonstrating characteristic ‘microgeodes’ of the affected phalanges and MRI highlighting occult disease as florid bone marrow oedema. Biopsy is not recommended as the diagnosis is made on imaging, negating the need for invasive procedures. The clinical and radiological features will often both resolve within 3–6 months, with complications such as pathological fractures rarely occurring, although seasonal recurrence has been reported.^{4 7}

Case presentation

This 43-year-old Caucasian woman presented to clinic with atraumatic swelling and bruising of the dorsolateral aspect of her left foot. The onset of symptoms was sudden during an extremely cold winter while working outdoors for several hours. Symptoms subsequently persisted for several days, with a worsening of the swelling over the lateral aspect of her foot with associated numbness and pain, which was exacerbated with weight bearing. The patient had no significant medical history and was not using any regular medications prior to simple analgesia for the new foot pain. The patient performed recreational exercise but with no history of recent trauma to explain the symptoms. There was no relevant social or family history.

During the acute worsening of the symptoms, she had attended the Accident and Emergency department where routine blood tests were performed with normal full blood count, renal function and liver function tests. AP and lateral radiographs of the affected foot (figure 1), venous ultrasound Doppler of the left leg and ECG were normal. On examination in clinic, there was bruising over the lateral aspect of the proximal, dorsal left foot with some associated discolouration (figure 2). There was also pain on palpation over the fifth metatarsal. Due to the persistent symptoms and lack of clear cause, an MRI scan of her left foot as well as weight-bearing radiographs were performed.

Figure 1.

AP radiographs of both feet at time of the acute presentation. The distal phalanges appear unremarkable with no features of phalangeal microgeodic syndrome radiographically.

Figure 2.

Photograph of the symptomatic left foot showing discolouration and swelling over the dorsolateral aspect.

MRI of the symptomatic left foot revealed extensive high signal changes within the distal phalanx of the left great toe (figure 3) as well as the tufts of the distal second and third toes suggestive of transient bone marrow oedema (figure 4). No focal abnormality was identified over the lateral aspect of the foot, at the site of her symptoms. A suspicion of PMS was raised and MRI of the contralateral, asymptomatic foot was recommended as well as a focused ultrasound of the area of swelling over the lateral foot. These demonstrated florid bone marrow oedema involving the right distal second, third and fifth toes, similar to the appearances of the left, further increasing suspicion of PMS. Ultrasound of the focal area of swelling demonstrated a resolving haematoma with associated soft-tissue changes and a possible feeding vessel. Due to the previously described association with systemic lupus erythematosus (SLE), the patient was referred to rheumatology for further assessment.

Figure 3.

Sagittal T1-weighted (A) and STIR-weighted (B) MRI slices of the left foot demonstrating diffuse low signal on T1 (arrowed) and florid STIR hyperintense signal (arrowed) in the distal phalanx of the great toe consistent with transient bone marrow oedema.

Figure 4.

STIR-weighted (A) and T1-weighted (B) MRI axial slices of the left foot. Florid STIR hyperintense and T1 hypointense signal in the distal phalanx of the great toe in keeping with transient bone marrow oedema (arrowed). Further, STIR-hyperintense and T1-hypointense signal in the tufts of the distal phalanges of the second and thirdtoes (dotted arrows).

Autoimmune screen performed by the rheumatology team demonstrated normal rheumatoid factor, and was negative for ANA, dsDNA, ENA and anti-CCP. ASO titre and ESR was normal. Vitamin D levels were 61 ng/mL and clotting screen was normal. Serum ACE and chest radiograph did not demonstrate any evidence of sarcoidosis.

Outcome and follow-up

Conservative management aimed at keeping her feet warm with use of adjuncts such as heated socks and as-required paracetamol with ongoing monitoring of her symptoms was recommended. Given the highly suggestive MRI appearances and the exclusion of key differential diagnosis and associated connective tissue disorders, a diagnosis of PMS was made.

Discussion

PMS is a rare, self-limiting condition, often seen in paediatric patients, characterised by pain and swelling in the fingers and toes.^8–10 Over 90% of reported cases affect the fingers, with a small number of cases affecting the toes, and rarely bilaterally.¹¹ Symptoms appear to be precipitated by cold temperatures but not exclusively, with some case reports not reporting such an association.^{1 12} PMS was first described by Maroteux in 1970 in a cohort of five infants presenting with frost-bite symptoms of the phalanges.³ The incidence appears to be higher in the Asian population with the vast majority of published case reports to date described in Japanese patients.2 3 5 13 14 The incidence rate of this disease remains unclear, but more recent case series suggest peak incidence between 4.5 and 10.3 years in Japanese cases, and as young as 2 years in European cases with no significant gender predilection.6 7 14 15

Adult-onset PMS is particularly rare and to our knowledge this is the fifth reported case in the literature, the second to affect the lower limbs rather than upper limbs and the first in a patient not of Japanese origin.^{1 5 16} The two cases presented by Nishino et al were in otherwise healthy women presenting with bilateral finger pain in the winter.⁵ The case presented by Kurushima et al was similarly in a woman presenting with painful fingers in the winter although a diagnosis of SLE was also established in her case.¹⁶

The pathophysiology of PMS is poorly understand and is hypothesised to be secondary to transient disturbance of the peripheral circulation and excessive vasoconstriction due to cold temperatures.¹⁷ This appears to most commonly affect the index and middle fingers, with involvement of the middle phalanx, followed by proximal phalanx and distal phalanx in decreasing frequency.^{4 14} PMS in the feet is less frequently reported but demonstrates similar imaging findings.^{10 17} Involvement of the metatarsals and metacarpals has been reported least frequently.^{4 14} It has been suggested that PMS may be analogous to frostbite but a consequence of less marked cooling.^{1 4} Older literature and case reports suggested an underlying infectious aetiology, but this has been largely dismissed as most paediatric patients had no focal infective symptoms.¹ Other authors have postulated an allergic aetiology¹⁵ or an immune response secondary to a foreign body.¹⁸

Histological examination of biopsied lesions in paediatric cases reveal a process of osteonecrosis with fibrous connective tissue proliferation as well as new bone formation.^{6 19} These appearances are likely secondary to the vasculopathy caused by cold temperature exposure.⁶ Radiological appearances are now felt to be pathognomonic on imaging and invasive procedures in this patient group is not advised.6 15 20 21

On plain radiographs, classical PMS may present with mild osteosclerosis with cortical irregularity and multiple well-defined foci of radiolucency due to osteolysis in the diaphysis.⁶ The name of the condition is subsequently derived from the classic radiographic findings of small osteolytic foci, measuring up to 1 mm in the diaphysis, described as a ‘microgeode’ by Maroteux.^{3 20} In some cases, metaphyseal transverse lucent bands may be seen as well as periostitis.⁶ Radiographic appearances usually return to normal within 6 months; however, secondary epiphysial damage may persist.¹ The findings on plain radiograph, however, may be entirely normal as in our case and previous case reports.⁵

MRI is particularly useful in diagnosis and demonstrates diffuse T1-hypointense signal and STIR-hyperintense signal in the affected phalanges in keeping with bone marrow oedema.^{2 22} Soft-tissue swelling is often observed in association, but joint effusions are atypical.⁶ Contrast-enhanced T1-weighted images demonstrate marked enhancement in the affected digits, with occasional small areas on non-enhancement, likely due to focal necrosis.^{2 22} Bilateral involvement is present in approximately one-third of cases, even if asymptomatic, as in our presented case.⁴ Overall, MRI is subsequently more sensitive at diagnosing radiographically occult disease, while negating exposure to ionising radiation.^{2 15 22} The differential diagnosis for these appearances includes osteomyelitis, tuberculous osteitis, osseous sarcoidosis and chronic multifocal osteomyelitis which all need to be considered and excluded clinically.¹

Patients generally require no intervention and symptoms regress spontaneously within 3–6 months with excellent prognosis clinically with radiological resolution lagging behind.^{4 14} Complications are rare, but a case of a secondary pathological fracture has been described,²² as well as digital shortening and angulation which may be secondary to growth plate injury.^{2 13 14} Cases of recurrence, however, have been described in the literature and tend to happen in the winter months.⁵

Learning points.

• Phalangeal microgeodic syndrome (PMS) is a rare, benign, self-limiting condition typically affecting the hands and feet of children but may affect adults and is thought to be due to impairment of peripheral circulation.

• Imaging features on plain radiographs (when present) and MRI are pathognomonic but not well recognised, particularly in Europe and North America.

• Differential diagnosis for the MRI appearances that should be considered include osteomylitis, tuberculosis, sarcoidosis and chronic multifocal osteomyelitis that can often be excluded clinically/biochemically.

• Recognising PMS clinically and radiologically is crucial to avoid invasive diagnostic procedures.