Description
A Japanese woman in her 70s, right-handed and immunocompetent, presented with a 2-month history of a palpable mass on the volar aspect of her right wrist. Contrast-enhanced MRI demonstrated a lesion surrounding the flexor digitorum profundus tendon of the index finger, appearing hypointense on T1-weighted images with peripheral enhancement (figure 1) and heterogeneously hyperintense on T2-weighted images (figure 2). Differential diagnoses included tenosynovial chondromatosis, malignant tumour and inflammatory mass, prompting surgical exploration.
Figure 1. Contrast-enhanced MRI of the right wrist. T1-weighted image showing a hypointense lesion surrounding the flexor digitorum profundus tendon of the index finger with peripheral enhancement.
Figure 2. Contrast-enhanced MRI of the right wrist. T2-weighted image demonstrating a heterogeneously hyperintense lesion around the flexor digitorum profundus tendon.
Intraoperatively, after incising the carpal tunnel, yellow, viscous fluid and numerous yellowish-white, rice-like bodies were observed (figure 3). Surgical incision, irrigation and debridement were performed. Histopathology revealed epithelioid granulomas with Langhans-type giant cells, and the rice bodies were identified as fibrin clumps (figure 4). On postoperative day 16, mycobacterial culture using liquid media became positive, and the isolate was identified as Mycobacterium intracellulare by DNA–DNA hybridisation assay, establishing the diagnosis of granulomatous flexor tenosynovitis.
Figure 3. Intraoperative findings after carpal tunnel incision. Yellow, viscous fluid and numerous yellowish-white, rice-like bodies were observed around the flexor tendon sheath.
Figure 4. Histopathological findings of the excised tissue. Epithelioid granulomas with Langhans-type multinucleated giant cells and fibrin clumps corresponding to rice bodies (H&E stain).
Combination therapy was initiated with azithromycin and ethambutol, followed by rifabutin. However, rifabutin-induced rash required modification to azithromycin, ethambutol and levofloxacin. As drug susceptibility testing for non-tuberculous mycobacteria (NTM) was unavailable at our institution, treatment decisions were guided by clinical response and established Mycobacterium avium complex (MAC) guidelines. Although optimal therapy duration for extrapulmonary MAC remains undefined, pulmonary disease guidelines recommend 12 months post-culture conversion.1 A positron emission tomography CT (PET-CT) at 9 months showed residual uptake, prompting extension of therapy. At 21 months, PET-CT confirmed complete resolution, and treatment was discontinued. Wrist function remained intact throughout.
NTM infections predominantly involve the lungs; musculoskeletal disease accounts for approximately 3% of cases.2 Upper extremity involvement, especially granulomatous flexor tenosynovitis, is the most common musculoskeletal manifestation.3 Mycobacterium marinum is typically implicated (82%), whereas M. intracellulare represents 3%.4 However, in reported NTM tenosynovitis cases with rice body formation, M. intracellulare comprised 58.8%, for unclear reasons.5 Transmission usually follows direct inoculation via trauma, puncture or surgical wounds; haematogenous spread from pulmonary sites is less common except for immunocompromised individuals.6 In this case, repeated minor injuries from dishwashing likely served as the portal of entry.
Rice bodies are a rare manifestation of synovial inflammation characterised by fibrin deposition.7 In NTM infections, they are usually localised to the flexor tendon sheath rather than diffuse synovitis seen in rheumatoid arthritis.8 NTM tenosynovitis is frequently diagnosed late due to low clinical suspicion and limitations in culture techniques. Diagnostic delays average 4 months and may be up to 36 months, correlating with poorer outcomes.9 This case underscores the importance of considering NTM, particularly M. intracellulare, in chronic granulomatous flexor tenosynovitis with rice body formation. Prompt recognition and early initiation of therapy are essential to prevent functional impairment and optimise prognosis.
Patient’s perspective.
I was worried because the mass on my wrist had been getting larger over the past two months. Since the hospital I visited couldn’t determine the cause, I wanted to get a clear diagnosis and proper treatment.
Learning points.
Mycobacterium intracellulare can cause tenosynovitis, typically presenting as granulomatous flexor tenosynovitis with rice body formation.
NTM tenosynovitis is often associated with minor injuries in occupations like dishwashing, where trauma to the hands is common.
Rice bodies, which are fibrin clumps, are a key diagnostic feature in cases of NTM-related tenosynovitis.
Footnotes
Funding: The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Case reports provide a valuable learning resource for the scientific community and can indicate areas of interest for future research. They should not be used in isolation to guide treatment choices or public health policy.
Provenance and peer review: Not commissioned; externally peer reviewed.
Patient consent for publication: Consent obtained directly from patient(s).
References
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