Tuberculosis continues to be a major debilitating disease in the endemic areas of developing nations, and it is staging a comeback in the developed countries of the world1,2. Many factors, including the emergence of human immunodeficiency virus (HIV) infection, an increasing number of patients receiving immunosuppressant medications, the emergence of resistant strains of tuberculosis, migrants to nonendemic areas, and exposure of health care providers to tuberculosis, have all contributed to the increasing magnitude of this problem1,3,4. Tuberculosis infection typically follows a protracted course, with subclinical infection flaring up during periods of immunosuppression. Osteoarticular infection accounts for only 1% to 3% of all cases of tuberculosis reported worldwide; of these cases, only 8% to 10% involve the foot3,5. With tuberculosis of the foot, the calcaneus is the most common bone to be affected3,6, and, to the best of our knowledge, very few cases of tuberculous osteomyelitis of the metatarsals have been reported in the literature. In a review of the English-language literature, we were able to identify thirty-five reported cases3-8. The first and fifth metatarsals are affected more commonly than others, both by pyogenic and tubercular infections4,7,9. The relatively exposed position of these metatarsals in the forefoot, combined with the increased weight-bearing stresses of the medial and lateral columns of the foot, likely make them more susceptible to repeated microtrauma and bacterial seeding3,10.
A patient with metatarsal tuberculosis usually presents with pain and swelling of the forefoot and difficulty with walking. There may be nonhealing ulcers and sinuses of varying extent and duration. The sinuses may be discharging serous or serosanguineous fluid. Tuberculous osteomyelitis of the metatarsals is usually secondary to lymphohematogenous spread from a pulmonary lesion, but in some cases, the primary site of tuberculosis may not be discernible. Extensive tubercular destruction of a metatarsal may lead to pathological fracture, which may be the presenting feature in some cases8,11.
The infection may block the nutrient artery, causing sequestration of the entire metatarsal shaft. The periosteal blood supply then becomes more active and starts to form layers of a reactive involucrum of bone, especially in children, giving rise to the “spina ventosa” form of tuberculous dactylitis3. Diffuse marrow involvement may result in a “cystic” form of metatarsal tuberculosis with intramedullary cavitations, or it may result in a “sieve” form with multiple small openings in the bone, connecting with discharging ulcers and sinuses on the skin surface7,8. Localized infection may result in an eccentrically located area of cavitary destruction with or without the presence of a “feathery” sequestrum.
The blood supply of the first metatarsal head enters chiefly through a leash of vessels on the plantar-lateral aspect of its neck12. Sometimes, the tuberculous process may block this vascular supply and cause a large area of the sesamoid-articulating plantar aspect of the first metatarsal head to undergo necrosis. This finding of a “large” tuberculous sequestrum was noted in our patient in Case 2. Similar seqeustra have been reported to occur in the tarsal bones3 but have never, to our knowledge, been reported in a metatarsal.
Chest radiographs demonstrate a concomitant suspicious lesion in 15% to 20% of cases of osteoarticular tuberculosis4. In order to prove that a lesion is of tuberculous origin, it is necessary to demonstrate granulomatous inflammation with caseating necrosis on histopathology or to culture Mycobacterium tuberculosis from tissue specimens from the site of infection. Tissue for diagnosis can be obtained by core biopsy or by open biopsy during a surgical intervention. Common diagnoses that mimic the clinical and radiographic picture of metatarsal tuberculosis include chronic pyogenic osteomyelitis, Brodie abscess, fungal osteomyelitis (especially Madura foot), enchondroma, and ganglion.
Once the diagnosis of tuberculosis has been confirmed, antitubercular chemotherapy is administered for a ten to twelve-month period. The sinuses usually heal within four weeks, “feathery” sequestra revascularize and become incorporated, and the affected bone shows mineralization, usually by six months. If the radiograph shows progressive destruction of the metatarsal at six months after treatment, nonresponsiveness to the antitubercular medications should be considered, and additional investigation is warranted. Nonresponsiveness may be the result of drug resistance, an immunocompromised state, or a nontubercular disorder3. Metatarsal tuberculosis surgery is indicated for removal of a “large” tuberculous sequestrum, as well as for biopsy and culture when there is uncertainty about the diagnosis and in some cases of pathological fracture of the metatarsal.
Tuberculous osteomyelitis of a metatarsal is a very rare condition, and the diagnosis may be missed until its course is quite advanced. A lack of awareness of this possible etiology, combined with a varying clinical and radiographic picture, can result in delayed diagnosis. This literature review, along with the presentation of our two cases, may aid the clinician when considering tuberculosis of a metatarsal as a potential diagnosis in a patient with foot swelling as well as pain of insidious onset and slow progression.