A rare actinomycosis of humerus: An unusual location and a diagnostic dilemma. A case report

Background: Isolated actinomycosis of the humerus is a very rare entity. Method: A 30-year-old male had an erythematous plaque with a pus-(minimal) discharging sinus over left lower arm. The patient had no discharge of sulphur granules from the sinus. The patient had raised ESR with a single lytic lesion with minimal sclerosis and inconspicuous periosteal reaction on radiographs. Such atypical clinical and radiological features lead to initial wrong diagnosis of tuberculosis. A diagnosis of Actinomycosis of humerus became possible after demonstration of filamentous bacilli in culture and on histopathology from the sulphur grains obtained by open biopsy. Result: The patient recovered completely after administering PenicillinG 24 million units intravenous for 7 days followed by 1.2 g of oral amoxicillin in three divided doses for 3 months and did not show any recurrence during last 2 years of follow up. Conclusion: Surgeons should be aware of this rare entity and difficulty in its diagnosis due to its variable manifestations, including confusion with highly endemic tuberculous infection. Awareness of full spectrum of the diseases and careful evaluation in individual cases will expedite diagnosis and avoid unnecessary surgical interventions.