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Dermatology Diagnosis

When A Patient Has Multiple Painful Sores On The Foot

A 46-year-old female patient presented to the Maricopa Medical Center Emergency Department in Phoenix with the complaint of multiple painful sores on her right foot that drain occasionally. She reported having problems with her foot for the past 11 years. The problems reportedly started with a small lump on the bottom of her foot and eventually spread over the entire foot. She reported burning pain and recent difficulty walking. Previous treatment for her skin condition took place in Mexico many years ago and included a short course of an unknown antibiotic, which resulted in minimal improvement.  

The patient had a past medical history remarkable for hypertension, high cholesterol and uncontrolled diabetes. Her daily medications included metformin, glyburide, simvastatin and lisinopril. She reported an allergy to penicillin. The patient denied any prior surgeries. Her social history was negative for alcohol consumption or smoking.  

The physical exam revealed a well-appearing female in no apparent distress. The neurovascular exam revealed strong, palpable pedal pulses with intact protective sensation. The patient exhibited equal and symmetric deep tendon reflexes. Gross visualization of her right foot revealed edema with tumefaction of the soft tissues as well as pustules on the plantar and dorsal foot.

A detailed dermatologic exam revealed soft tissue swelling circumferentially to the right mid- to distal foot. Multiple pustules were present with draining tracts. Tiny granules were present in these draining sinuses. The majority of the nodules were plantar from the medial arch and extending distal laterally. Only a few small indurated nodules were on dorsal aspect of the foot. There was severe pain on palpation of the pustules. There was no surrounding erythema or fluctuance to the right foot.

Key Questions To Consider

1)    What are the differential diagnoses?
2)    What is the most likely diagnosis?
3)    What are the key characteristics of this condition?
4)    What is the gold standard method of diagnosis?
5)    What is the proper treatment and follow up?

Answering The Key Diagnostic Questions

1) Chronic bacterial osteomyelitis, pustular psoriasis, tuberculosis and Buruli ulcer, and deep fungal infections such as blastomycosis, coccidioidomycosis, leishmaniasis, syphilis and Madura foot (mycetoma)1
2) Madura foot
3) Spreading pustules with grains that recur along with firm soft tissue swelling and induration2  
4) Soft tissue biopsy, culture and Gram stain2
5) Treatment involves surgical debridement followed by prolonged appropriate antibiotic therapy for several months until resolution of symptoms. Resistant cases may require combination therapy of trimethoprim-sulfamethoxazole, dapsone and streptomycin.

Essential Insights On The Differential Diagnosis

Differential diagnoses should include chronic bacterial osteomyelitis, pustular psoriasis, tuberculosis, Buruli ulcer and deep fungal infections such as blastomycosis, coccidioidomycosis, leishmaniasis and syphilis.1 Biopsy is required for proper diagnosis.2  

Osteomyelitis is an inflammation of bone caused by a pyogenic organism. Osteomyelitis is categorized as acute, subacute or chronic as well as medullary, superficial, localized or diffuse. Localized bone pain, erythema and drainage around the affected area are frequently present. The cardinal signs of chronic osteomyelitis include erythema, edema, draining sinus tracts, visible or palpable bone, deformity and/or instability of the bone/joint segment.3

Pustular psoriasis is a rare inflammatory skin condition that can lead to widespread sterile pustules. Palmoplantar pustular psoriasis is limited to hands and feet versus generalized pustular psoriasis, which can affect the entire body. Clinically, one would see skin becoming dry, bright red and tender. Large yellow pustules up to 5 mm in diameter on palms of hands and soles of feet can be visible. This condition is cyclical with new crops of pustules forming while older pustules dry up, turn a brown color and then gradually diminish. These pustules do not lead to sinus tracts. This form of psoriasis affects approximately 5 percent of people with psoriasis. Systemic symptoms may be present with fever, chills and constitutional symptoms.4

Cutaneous tuberculosis may lead to nodules, lumps, ulcers and abscesses in the soft tissues. Extrapulmonary tuberculosis in the foot and ankle can cause deep tissue infections that can subsequently lead to swelling with fullness around malleoli and the Achilles tendon insertion. There may be a discharging sinus or non-healing ulcer with secondary infection. The most commonly involved bones in the foot are the calcaneus, talus, first metatarsal and navicular. The midtarsal joint is the most common associated area in the foot.5

Buruli ulcers are caused by Mycobacterium ulcerans. The dermatologic lesions start as a painless nodule. Over time, the lesion will ulcerate and become a large necrotic ulceration with undermined edges. Local immunosuppressive properties of the mycolactone toxin enable the disease to progress with no pain and fever. This condition rarely affects bone.6

Blastomycosis is caused by an infection with Blastomyces dermatitidis, which is a fungal infection that occurs primarily in the lungs. Cutaneous blastomycosis presents as an erythematous, indurated lesion with central ulceration, usually presenting with tenderness. Approximately 15 to 60 percent of patients with systemic blastomycosis have skeletal involvement. Blastomycosis is endemic in the Ohio and Mississippi River valleys. In addition to dermatologic manifestations, there are systemic conditions of flu-like symptoms with fever, chills, arthralgias, headache and cough.7

Coccidioidomycosis is a fungal infection caused by the organism Coccidioides immitis. The infection is endemic to the San Joaquin Valley, which includes parts of California, Arizona and Mexico. It is primarily a lung infection. However, like tuberculosis, it can infect other tissues of the musculoskeletal system, including the skin, soft tissues, bones and joints. The skin can develop papules, abscesses or pustules. Infections in the synovial lining and joints may lead to arthralgia and periarticular edema. Infections in the bone can occur in up to 50 percent of patients with the disseminated disease.8

Localized cutaneous leishmaniasis is a disease that arises in the tropics, subtropics and southern Europe. The parasitic disease is caused by a bite of an infected sand fly. Dermatologic presentation includes papules, nodules, plaques or noduloulcerative lesions.9 People who develop clinical evidence of infection usually develop papules or nodules that can change in size and appearance over time. These lesions may progress into ulcerations that may or may not be painful.10  

Syphilis is caused by the bacteria Treponema pallidum. Once infected, there is an incubation period of anywhere from 10 to 90 days (on average 21 days) before any signs become apparent. Initially, primary syphilis appears as a painless ulcer or chancre where the infection originated. Flu-like symptoms occur and widespread rash appear with secondary syphilis, which can present itself on the skin of the foot and ankle.11  

Mycetoma, commonly referred as Madura foot, is a chronic infection of subcutaneous tissues. Mycetoma is endemic in Africa, Mexico and India. A fungus or bacteria may cause mycetoma.1 Fungal Madura foot can initially present as an inconspicuous rash with only minor pruritus and can mimic other soft tissue dermatologic conditions. The incubation period of Madura foot can lead to misdiagnosis and improper treatment during the initial stages. Sinuses develop after six to 12 months with extension to the underlying fascia, muscle and bone.12,13

A Guide To Making A Proper Diagnosis Of Madura Foot

Madura foot is characteristically defined as soft tissue swelling with painful nodules and sinuses that drain white to yellow fluid.12 Tiny grains or granules may be visible in the drainage of the sinuses. The typical presentation includes a lesion on the plantar aspect of foot (where the patient contracted the infection) that subsequently spreads to the entire foot.14

Madura foot is caused by either a true fungi (eumycetoma) or by a filamentous bacteria (actinomycetoma).15 Proper diagnosis is necessary as the treatments for these two variants differ.1 Soft tissue biopsy is the gold standard for proper diagnosis of skin conditions.2 Microbiology analysis with culture, including fungal and acid-fast bacilli (AFB), and Gram stain is indicated. When bone is involved, pathological analysis is also helpful in diagnosis.16  

Histologically, H and E stains of the subcutaneous tissues show suppurative granulomas with neutrophils surrounding the characteristic grains in the subcutaneous tissues. The occasional multinucleated giant cells may also be present. H and E and Gram stains show thin filamentous bacteria in cases of actinomycetoma and thick club-shaped structures in eumycetoma.2

Pertinent Pearls On Treating Madura Foot

The mainstay for treatment of Madura foot caused by actinomycetoma includes surgical debridement followed by prolonged appropriate antibiotic therapy for several months until resolution of symptoms. Resistant cases may require combination therapy of trimethoprim-sulfamethoxazole, dapsone and streptomycin.17 Failure of adequate treatment can lead to chronic osteomyelitis, which may necessitate chronic lifelong therapy or amputation.18  

Per the patient’s medical records, physicians took the first biopsy of her soft tissue in Mexico in 2003, which revealed an “infection” with no organism growth. There was another biopsy of the right foot in 2009 and the histologic analysis showed whitish yellow “sulfur granules” with non acid-fast bacteria consistent with Madura foot. The patient was admitted to the hospital in 2011 with increased redness and swelling to her right foot with the diagnosis of Madura foot caused by Actinomyces species. Magnetic resonance imaging of the right foot showed osteomyelitis of the metatarsals. Bone biopsy confirmed a diagnosis of osteomyelitis of metatarsal bones.

The patient, who is allergic to penicillin, started on doxycycline for one year and experienced significant improvement of her condition. She will likely be on a lifetime maintenance regimen of antibiotics. The most recent follow-up examination of the plantar, dorsal and medial surfaces of the foot in 2017 shows improvement of nodules and soft tissue swelling.

In Conclusion

This case illustrates the presentation of a patient with painful pustular lesions on the foot. The key clinical features in this case to make the diagnosis included draining sinus tracts with grains, soft tissue swelling, firm induration/tumefaction of tissues and nodule formation. Wound culture and tissue biopsy results confirmed the diagnosis.

Patients usually contract Madura foot when they walk barefoot in dry or dusty areas. Minor trauma in the skin allows the inoculation of the pathogens. The incubation period varies from several weeks to months. Sinuses develop after six to 12 months with common extension to the underlying fascia, muscle and bone. Differential diagnoses for pustular lesions should include chronic bacterial osteomyelitis, pustular psoriasis, tuberculosis, Buruli ulcer and deep fungal infections such as blastomycosis, coccidioidomycosis, leishmaniasis and syphilis. Biopsy is required for proper diagnosis.

Dr. Chrisman is a third-year resident at Maricopa Medical Center in Phoenix.

Dr. Fishco is board-certified in foot surgery and reconstructive rearfoot and ankle surgery by the American Board of Podiatric Surgery. He is a Fellow of the American College of Foot and Ankle Surgeons, and a faculty member of the Podiatry Institute. Dr. Fishco is in private practice in Phoenix.


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Dermatology Diagnosis
Melissa Chrisman, DPM, and William D. Fishco, DPM, FACFAS
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