Mycobacterium haemophilum tenosynovitis of the thumb in an immunocompetent adult: a case report highlighting a diagnostic challenge.

Objective

We report a rare case of Mycobacterium haemophilum flexor tenosynovitis in an immunocompetent adult and discuss the diagnostic challenges posed by this organism under standard culture conditions. Patient and

Methods

A 72-year-old Japanese man presented with chronic pain and swelling of the left thumb following a rose thorn injury and subsequent exposure to aquarium water. Magnetic resonance imaging revealed an effusion in the flexor tendon sheath. The patient underwent synovectomy and debridement. Acid-fast bacilli staining of intraoperative specimens was negative, and liquid mycobacterial culture at 37°C remained negative after 6 weeks.

Results

Local symptoms persisted with recurrent tenosynovial effusions. A repeat aspirate showed growth on Mycobacteria Growth Indicator Tube culture after 5 weeks, and the isolate was identified as M. haemophilum using matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry. Symptoms resolved after drainage and oral antimicrobial therapy, with no recurrence at the 6-month follow-up.

Conclusion

M. haemophilum should be included in the differential diagnosis of distal-extremity tenosynovitis, particularly in patients with a history of contact with aquarium water. Negative cultures at 35-37°C does not exclude M. haemophilum infection. Close communication between clinicians and microbiology laboratories is essential to ensure appropriate culture conditions, including low incubation temperatures and iron/hemin supplementation.