Case Series of Three Cases of Madura’s Foot with a Characteristic ‘Dot in Circle’ Sign: A Radiologist Perspective
Correspondence Address :
Sadaf Sultana,
Flat No. 305, IT Grand Apartmemt, Zakariya Market, Medical Road, Aligarh-202001, Uttar Pradesh, India.
E-mail: drsadafsultana@gmail.com
Madura’s foot is a rare infectious granulomatous disease affecting the foot. The incidence of this disease has decreased in recent years due to improved living conditions. However, it can still be misdiagnosed by inexperienced surgeons as other similar conditions. Early and accurate diagnosis is crucial for optimal treatment and limb preservation. In this study, the authors present three unusual cases of Madura’s foot. A 23-year-old woman presented with swelling and draining sinuses in her left foot for six years. Imaging tests including Ultrasonography (USG), Computed Tomography (CT), and Magnetic Resonance Imaging (MRI) revealed the characteristic ‘dot in circle’ sign of Madura’s foot. However, her USG-guided biopsy did not confirm the diagnosis, and it was only through an excisional biopsy that actinomycetoma was confirmed. Another case involved a 60-year-old male with multiple soft tissue swellings on his right foot for 10 years, resulting in foot deformity. Radiographs showed multiple punched-out lytic lesions in the bones, while USG and MRI exhibited the typical ‘dot in a circle’ sign. Histopathological examination confirmed actinomycetoma. The third case involved a 36-year-old male with a chronic sinus discharging yellow pus and black granules on the volar side of his right foot. USG and MRI revealed the classic signs of Madura’s foot, and these findings were correlated with histopathological examination. The present cases confirm the specificity of the ‘dot-in-circle’ sign on MRI and USG, supported by histopathological correlation.
Actinomycetoma, Granulomatous, Mycetoma, Ultrasonography
Mycetoma is a chronic, slowly developing granulomatous infection that affects the skin and subcutaneous tissue. Its primary symptoms include swelling, discharge-producing sinuses, and granules in the discharge. The infection typically occurs through penetrating injuries or repeated minor trauma (1). The foot and hand are the most commonly affected sites (2). While microbiological culture and biopsy are reliable diagnostic methods, they can be time-consuming and may not provide a definitive diagnosis for organisms with complex nutritional requirements that are difficult to grow on standard culture media (3).
Case 1
A 23-year-old female patient presented to a tertiary care centre in Northern India with multiple swellings and draining sinuses on the dorsal aspects of her left foot, which had been present for six years (Table/Fig 1)a. On examination, the patient had no fever or palpable nodes in the regional areas. The dorsal aspect of the left foot showed black discoloration, several ill-defined swellings, and multiple non-tender sinuses with yellowish discharging grains. Culture and sensitivity testing of the purulent discharge revealed Staphylococcus aureus with no fungal growth. Conventional Radiograph (CR) of the left foot showed soft tissue prominence on the dorsal aspect (Table/Fig 1)b. Ultrasonography (USG) revealed the characteristic ‘dot in circle’ sign with surrounding inflamed fat (Table/Fig 1)c. Non-Contrast Computed Tomography (NCCT) depicted superficial erosions of multiple metatarsals (Table/Fig 2)a-d. Magnetic Resonance Imaging (MRI) of the left foot revealed multiple nodular lesions with a peripheral rim, creating a target-like “dot-in-circle” appearance (Table/Fig 2)e.
The patient was treated with the Modified Welsh regimen, consisting of three cycles of intravenous Amikacin (500 mg) for 21 days each, followed by a four-week regimen of oral Trimethoprim (160 mg) - Sulfamethoxazole (800 mg) combination twice a day. Medical treatment resulted in complete recovery of all sinuses. The patient later underwent surgery (Table/Fig 3)a-c and continued the oral Trimethoprim 160 mg - Sulphamethoxazole 800 mg combination twice a day, along with Rifampicin 600 mg once a day for one month.
The excised specimen was sent for histopathological examination (Table/Fig 4)a,b. The histopathological findings showed dense suppurative granulomas surrounding the Actinomyces colony and radiating filamentous organisms, confirming actinomycetoma (Table/Fig 4)c,d. The patient remained symptom-free for six months after surgery (Table/Fig 3)c and has been regularly followed-up for the past two years without recurrence of symptoms. The patient expressed satisfaction with the treatment.
Case 2
A 60-year-old male farmer presented to the plastic surgery department and radiology department of a tertiary care centre in Northern India with multiple soft tissue swellings on the dorsal aspect of his right foot, along with progressive deformity, for 10 years (Table/Fig 5)a,b. The patient initially experienced painless swelling, which gradually grew in size. Over the past two years, the swelling has caused difficulty in walking, wearing footwear, and continuing farming activities. The swelling eventually led to foot deformity.
On examination, the patient had no fever or lymphadenopathy. The dorsal aspect of the right foot showed discolouration, multiple swellings with ill-defined borders, and non-tender firmness without fluctuation. Several draining sinuses were also present. Conventional Radiograph (CR) of the right foot showed soft tissue prominence with multiple punched-out lytic lesions in the tarsal and metatarsal bones, along with toe deformity (Table/Fig 6)a,b. The post-operative follow-up clinical image of the patient is shown in (Table/Fig 6)c. Ultrasonography (USG) and Magnetic Resonance Imaging (MRI) showed the characteristic ‘dot in circle’ sign consistent with Madura’s foot (Table/Fig 7)a,b. Microbiological investigations were inconclusive. The patient was treated with oral Itraconazole 200 mg twice a day for six months, resulting in a decrease in the number of discharging sinuses. Below-knee amputation was advised, and the patient underwent the procedure. Pus culture revealed Staphylococcus aureus growth. Excisional biopsy of the lesion was sent for histological analysis, which showed giant cells with sulfur granules. Histopathological examination revealed balls of eosinophilic radiating filaments surrounded by dense mixed inflammatory infiltrates (Table/Fig 7)c. PAS staining showed positively stained colonies, confirming the diagnosis of eumycetoma. After one year of follow-up, the patient remained free of previous symptoms (Table/Fig 6)c. The patient expressed satisfaction with the treatment received.
Case 3
A 36-year-old male farmer presented to the dermatology department of a tertiary care centre in Northern India with a chronic sinus discharging yellow pus with black granules on the dorsal side of his right foot for six months, which started after a thorn prick on the foot. On examination, the patient had a normal temperature and no lymphadenopathy. Conventional Radiograph (CR) showed prominent soft tissue on the dorsal aspect of the foot (Table/Fig 8)a. Ultrasonography (USG) (Table/Fig 8)b and Magnetic Resonance Imaging (MRI) (Table/Fig 8)c depicted the classic ‘dot in circle’ sign of Madura’s foot. Pus culture revealed no growth, but cytology and biopsy (Table/Fig 8)d confirmed Actinomycetoma. The patient received antibiotic therapy for actinomycetoma (same as the first patient) for six months, followed by surgery. After completing the treatment, the patient was symptom-free with no residual sinus. During a three-year follow-up, the patient did not develop any new symptoms and expressed full satisfaction with the treatment.
In recent years, the “dot-in-circle” sign has emerged as a highly specific indicator of mycetoma on Ultrasound (USG) and Magnetic Resonance Imaging (MRI), allowing for non-invasive and early diagnosis (3). This unique sign has demonstrated the value of USG and MRI in diagnosing mycetoma at an early stage. USG, being a more affordable and widely available imaging modality, can be used as the first-line approach to confirm the diagnosis.
Mycetoma is a localised granulomatous infection of subcutaneous tissue caused by actinomycetes (actinomycetoma) or fungi (eumycetoma), commonly seen in Africa and Asia (4). Without timely intervention, mycetoma can result in lifelong disabilities (5),(6),(7).
Radiological imaging, including Conventional Radiograph (CR), USG, MRI, and Non-Contrast Computed Tomography (NCCT), is necessary to assess the extent of the lesions and aid in surgical planning (7),(8). CR is performed to determine if there is involvement of the bone, as non-surgical treatment becomes challenging in such cases (8). Advanced mycetoma can be identified on CR by radiological markers such as bone erosions, cavities, periostitis, bony sclerosis, and soft tissue edema (3). USG is a more specific imaging modality than CR for detecting mycetoma and is commonly used in its diagnosis (9). The “dot-in-circle” sign on MRI is characterised by a dot representing T2 hypointense (dark signal) fungal or actinomycete grains, and a circle denoting the peripheral T2 hyperintense (bright signal) abscess or granuloma with a thin peripheral hypointense line representing fibrous matrix (Table/Fig 9)a. The comparable USG “dot-in-circle” sign consists of circular hypoechoic lesions with a hyperechoic centre (Table/Fig 9)b (3).
Inflammatory tissue appears on MRI as groups of small (2 to 5 mm) spherical hyperintense lesions with hypointense centre that are surrounded by a thin dark (low-signal) ring that represents the intervening fibrous septa. A mycetoma appears to be strongly suggested by the “dot in circle” indicator (3),(7). MRI can better delineate the subcutaneous fat, bones, and muscle involvement precisely and thus can grade the disease, which affects the patient’s management (9). The differentials for the “dots” are phlebolith of haemangioma, though, clinical presentation, scarcer number of the dots, nonappearance of sinuses or inflammation in surrounding tissues favours the finding of slow flow vascular pathology. Other differentials are rice bodies in the fluid of joint or tendon infection, exclusively in tuberculosis or Rheumatoid patients (3). By using a CT scan, the bone involvement in mycetoma can be evaluated.
CR and USG imaging are suitable for local settings and are particularly useful in low-income countries. In advanced cases with bone involvement, surgical intervention is required for a therapeutic cure (5). Timely diagnosis of mycetoma is crucial to prevent functional impairment (10).
On USG, eumycetoma lesions appear as abundant sharp bright hyper-reflective echoes parallel to the dark grains, while actinomycetoma lesions show less discrete echoes due to smaller size and consistency (11). The “Welsh regimen,” which combines co-trimoxazole with amikacin in one to five-week cycles, has been suggested for use in resistant disease. Modifications of the original Welsh regimen may include adding rifampicin, dapsone, or increasing the number of cycles in cases of bony erosion (12). Oral itraconazole (400 mg divided into two doses for six months to three years) is the most commonly used treatment for eumycetoma. Oral antifungal therapy followed by surgical debridement is the preferred approach for treating eumycetoma (13). For a detailed comparison between actinomycetoma and eumycetoma, refer to the related articles and the provided tables (Table/Fig 10),(Table/Fig 11) (14),(15),(16),(17),(18),(19).
Ultrasound (US) and Magnetic Resonance Imaging (MRI) complement each other in the early diagnosis and confirmation of Madura’s foot, characterised by the “dot-in-circle” sign on imaging. These imaging modalities are quick, non-invasive, and simple to use for early diagnosis and assessing the extent of the lesion. While microbiological culture and biopsy are reliable diagnostic methods, they are time-consuming. In one of our patients, cytology and culture yielded false negative results, highlighting the diagnostic accuracy of low-cost and readily available USG imaging for making the diagnosis and initiating timely treatment with favourable clinical outcomes.
Contributors: All authors contributed to the case report. Dr. Mehtab Ahmad and Dr. Sadaf Sultana were involved in the patient’s diagnostic workup and management.
DOI: 10.7860/JCDR/2023/64076.18410
Date of Submission: Mar 14, 2023
Date of Peer Review: May 08, 2023
Date of Acceptance: Jun 23, 2023
Date of Publishing: Sep 01, 2023
AUTHOR DECLARATION:
• Financial or Other Competing Interests: None
• Was informed consent obtained from the subjects involved in the study? Yes
• For any images presented appropriate consent has been obtained from the subjects. Yes
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ETYMOLOGY: Author Origin
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