Teaching Case

A 31-year-old farmer born in Mali with no medical history of interest complained of a painless swelling in the right foot that had been present for the past 4 years. The patient had been treated with multiple antibiotics with no improvement of symptoms.

Plain radiograph of the foot demonstrates several osteolytic lesions in midfoot and hindfoot bones, areas of sclerosis and soft tissue swelling in plantar and dorsal surfaces of the foot. (Fig. 1)

Computed tomography shows in more detail the long-term bone destruction of the foot.
There are diffuse erosions along the midfoot and hindfoot and severe soft tissue inflammatory changes involving subcutaneous tissue, muscles and intermuscular fascial planes. (Fig. 2)

Magnetic resonance imaging was performed to characterize and evaluate the extent of the disease. T1WI post-gadolinium fat-saturated MRI reveals diffuse hyperintensity involving the majority of the bones of the foot secondary to marrow oedema. In addition, multiple small discrete spherical hyperintense lesions surrounded by low-signal-intensity rim are noted, some of them containing central dots, hypointense on all sequences, creating a nearly pathognomonic sign, called the “dot-in-circle”. (Fig. 3)

Ultrasonography images reveal multiple hypoechoic cavities with thickened walls containing small hyperechoic foci corresponding to mycetoma grains, forming the “dot-in-circle” sign. (Fig. 4)

Madura foot or mycetoma is a chronic granulomatous disease characterized by localized infection involving subcutaneous tissues, which can extend to underlying bone [1-8]. It was first described in Madura (India), hence the eponym [1-5].

The disease can be caused by two groups of organisms, eumyces and actinomyces [1-8]. Its prevalence is high in farmers aged 20-40 years who walk barefoot [1, 2, 4, 6, 7].

Madura foot is prevalent in tropical and subtropical regions [1, 2, 4, 5, 6, 7, 8] an area known as the Madura/Mycetoma Belt [6]. Nevertheless, as a result of the increasing phenomenon of immigration, cases are reported worldwide [2].

The anatomic region most commonly affected is the foot [2, 4, 6, 7], up to 70% of cases [2, 7], although involvement of the hand, head or back has also been described [2, 3, 6].

Clinically the disease follows an indolent but progressive course [2, 3, 4, 6]. The classic triad of subcutaneous nodules, draining sinuses and purulent granular exudates appears in later stages [2, 4, 6].

Early diagnosis is crucial to prevent morbidity and mortality [2]. However, diagnosis based on clinical suspicion is difficult and Mycetoma is not often considered unless the pathognomonic triad is present [2]. Identification of the causal agents with biopsy or microbiological culture is the gold standard [2, 5], however, as in our case, repeated attempts to culture the microorganism might fail, especially in fastidious organisms [2, 3]. This fact can contribute to a delay in diagnosis and may worsen the prognosis.

Imaging is a fast and affordable diagnostic tool which can offer a non-invasive diagnosis [2]. MRI is the modality of choice, not only to make an early diagnosis, but also to characterize and evaluate the extent of the disease and to discriminate mycetoma from other conditions [2]. The “dot-in-circle” sign has been reported as a highly specific sign for mycetoma [2]. It was first suggested by Sarris el al. (2003) who described it as multiple small (2-5 mm) lesions of high signal intensity surrounded by a low-intensity stroma (circle), and a small low-intensity focus (dot) in the centre [2, 3, 5, 8]. This sign, seen on MRI, is known to be pathognomonic of mycetoma and can be used to help in planning appropriate treatment strategies [2].

Treatment of mycetoma consists of combined long-term antibiotics agents and surgery, which can include amputation in advanced stages [1, 7]. Recurrence is quite common [4, 5, 7, 8].