Atypical Pott's disease: localized infection of the thoracic spine due to Mycobacterium avium-intracellulare in a patient without human immunodeficiency virus infection. (Case Report).

Abstract: Mycobacteriunz avium-intracellulare (MAI) rarely causes disease of the spine in healthy individuals. We describe an elderly woman who had isolated skeletal involvement with MAI, mimicking Pott's disease. She responded well to surgical excision of the inflamed tissue and antibiotic therapy. Osteomyelitis due to MAI must be differentiated from that due to Mycobacteriutn tuberculosis because the treatment regimens are different.

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The organism Mycobacteriunz avium-intracellulare complex(MAI) belongs to Runyon Group III nonchromogenic mycobacteria. Ubiquitously present in soil, water, and house dust, MAT was traditionally considered to have a low potential for causing infection in the normal human host. This perception has been modified as improved technology has allowed better identification of mycobacteria. MAI is now identified as an important pathogen in the population with acquired immunodeficiency syndrome (AIDS). MAL infection is increasingly found in patients with and without AIDS. The patients without AIDS tend to be elderly, have preexisting pulmonary disease, and have medical conditions that limit their immune response. We describe an elderly patient who had MAT infection of the spine without clinical evidence of pulmonary involvement or AIDS.

Discussion

Tuberculosis may involve any organ of the body. With the emergence of AIDS, extrapulmonary tuberculosis has increased from 10% of the total tuberculosis cases to 18-20% of the total cases. (1) The most frequent site of extrapulmonary involvement is skeletal tuberculosis, and 50% of these are spinal tuberculosis. Tuberculosis of the spine is popularly known as Pott's disease. In 1779, however, when Pott first described "lower leg palsy associated with abnormal curvature of the spine," he probably did not know that the disease is caused by M. tuberculosis. While MAI may cause lung disease in non-HIV-infected individuals, spinal involvement is extremely rare. (1,2) Bone involvement from nontuberculous mycobacteria (NTM) infection is generally due to trauma or surgical procedures (3,4) such as sternal wound infection after coronary artery bypass grafting. (5) Occasional outbreaks have been traced to nosocomial infection from equipment contamination. Lidocaine fluid, flexible endoscopy scopes, and hospital supplie s have been implicated in causing infection or disease from NTM. (6,7) Fortunately, such epidemics are rare.8 There have been a few case reports of joint cavities (knee joint, shoulder joint) infected with NTM after intraarticular injection of steroids or lidocaine. Contamination of the "sterile" bottles is suspected as the cause in such incidents. (9)

In the absence of trauma or a surgical procedure, vertebral infection with MAT in patients without AIDS is extremely rare. Zventina et al (10) reported a case of MAI that involved the shoulder and spine. Pirofsky et al (11) reported spinal infection in an elderly artist who died because of the delay in starting adequate therapy. Pombo et al (12) reported a case of disseminated MAI infection and osteomyelitis in a normal host; however, this patient did not have spinal involvement. Brodkin (13) described a case of paraspinal abscess that also mimicked Pott's disease. Chan et al (14) reported three cases of vertebral osteomyelitis due to NTM after blunt trauma. In their review of the medical literature from 1955 through 1977, they identified only 15 cases of NTM vertebral osteomyelitis. Importantly, not one was due to MAT. Weiner et al (15) published a case of a 70-year-old woman with MAT vertebral osteomyelitis and pulmonary involvement. We believe ours is the fifth report in the English language medical litera ture of spinal infection from MAI in a patient without HIV infection. Our patient also lacked any history of trauma or surgical procedure.

The absence of clinical and radiologic involvement of the lungs makes this current report more intriguing. The site of entry in such patients may be the gastrointestinal tract. Similar to other reported cases in the literature, our patient also had osteoporosis. Whether osteoporosis is a separate risk factor remains controversial. Long-term steroid therapy may cause osteoporosis, which was a common risk factor in all the previous cases of MAI vertebral osteomyelitis reported in the literature. Even though our patient was HIV negative, her immune status may not have been completely normal. She was receiving long-term glucocorticosteroid therapy for polymyositis, both of which may impair T lymphocyte function. (16) Nevertheless, this elderly patient responded well to the surgical drainage and anti-MAI therapy. This is in contrast to AIDS patients who are known to get infection from MAI when the T-cell count drops below 100/[mm.sup.3]. Many of them have gastrointestinal symptoms such as diarrhea, abdominal pain, and weight loss. Treating such cases is difficult, and outcome is frequently poor. Treating pulmonary infection in non-HIV-patients is also difficult because MAI is often resistant to most antituberculous drugs. Differentiating mere colonization from the true infection is also a challenging clinical dilemma. Multiple positive sputum cultures or tissue cultures are required to confirm the diagnosis.

Current therapy for MAI disease includes rifampin, ethambutol, and clarithromycin. (17,18) Our patient initially received standard antituberculous treatment because the diagnosis of Pott's disease was presumed in the early course of her illness. Although the patient responded to this treatment, appropriate modifications in therapy were made once the culture report of MAI became available. When MAI disease is localized, surgical excision is beneficial. Interestingly, refractory disseminated MAI disease may respond to interferon [gamma] (IFN-[gamma]) infusion. (19) Multifocal osteomyelitis from MAI was reported in three patients who had a genetic defect of the IFN-[gamma] receptor. (20)

Our patient's clinical picture of backache, fever, and abnormal findings on x-ray films of the spine was similar to that seen in Pott's disease. Although mycobacterial infection of the spine is most frequently due to M. tuberculosis, NTM may rarely cause infection of the spine. We hope this case report will remind the clinician that advanced age, chronic glucocorticosteroid therapy, malnutrition, and comorbid illness may contribute to immunosuppression that may lead to skeletal infection with MAI (Table 1). Awareness of this rare disease should help clinicians make a prompt diagnosis and initiate appropriate treatment.

Table 1

Risk factors for skeletal infection from Mycobacterium
avium-intracellulare complex


Trauma/foreign body
Surgical procedure/wound infection
Old age
Preexisting pulmonary disease
AIDS/HIV infection
Bone marrow transplant
Chronic steroid therapy
Osteoporosis
Osteoporosis
Immunocompromised host (eg, as a result of leukemia, radiotherapy,
 sepsis)

Accepted April 21, 2002.

References

(1.) Mehta JB, Dutt AK, Harvill L, Mathews KM. Epidemiology of extrapulmonary tuberculosis: A comparative analysis with pre-AIDS era. Chest 1991;99:1134-1138.

(2.) Nightingale SD, Byrd LT, Southern PM, Jockusch JD, Cal SX, Wynne BA. Incidence of Mycobacterium avium-intracellular complex in human immunodeficiency virus-positive patients. J Infect Dis 1992;165:1082-1085.

(3.) Falkinham JO. Epidemiology of infection by nontuberculous mycobacteria. Clin Microbiol Rev 1996;9:177-215.

(4.) O'Brien RJ, Geiter LJ, Snider DE. The epidemiology of nontuberculous mycobacteria diseases in the United States: Results from a national survey. Am Rev Respir Dis 1987;135:1007-1014.

(5.) American Thoracic Society. Diagnosis and treatment of disease caused by nontuberculous mycobacteria. Am J Respir Crit Care Med 1997; 156(Suppl 2):S1-S25.

(6.) Bennett SN, Peterson DE, Johnson DR, Hall WN, Robinson-Dunn B, Dietrich S. Bronchoscopy-associated Mycobacterium xenopi pseudoinfections. Am J Respir Crit Care Med 1994;150:245-250.

(7.) Hellinger WC, Smilack JD, Greider JL Jr, Alvarez S, Trigg SD, Brewer NS, et al. Localized soft tissue infections with Mycobacterium avium/Mycobacterium intracellular complex in immunocompetent patients: Granulomatous tenosynovitis of the hand or wrist. Clin Infect Dis 1995;21:65-69.

(8.) Wallace RJ Jr, Musser JM, Hull SI, Silcox VA, Steele LC, Forrester GD, et al. Diversity and sources of rapidly growing mycobacteria associated with infections following cardiac surgery. J Infect Dis 1989;159:708-716.

(9.) Desplaces N, Picardeau M, Dinh V, Leonard PH, Mamoudy P, Raguin G, et al. Spinal infections due to Mycobacterium xenopi after discectomies. Presented at the 35th Jnterscience Conference on Antimicrobial Agents and Chemotherapy, San Francisco, CA, 1995 (Abstract J162).

(10.) Zvetina JR, Demos TC, Rubinstein H. Mycobacterium intracellulare infection of the shoulder and spine in a patient with steroid-treated systemic lupus erythematous. Skeletal Radial 1982;8:111-113.

(11.) Pirofsky JG, Huange CT, Waites KB. Spinal osteomyelitis due to Mycobacterium avium-intracellulare in an elderly man with steroid-induced osteoporosis. Spine 1993;18:1926-1932.

(12.) Pombo D, Woods ML II, Burgert SJ, Shumsky IB, Reimer LG. Disseminated Mycobacterium avium complex infection presenting as osteomyelitis in a normal host. Scand J Infect Dis 1998;30:622-623.

(13.) Brodkin H. Paraspinous abscess with Mycobacterium avium-intracellulare in a patient without AIDS. South Med J 1991;84:1385-1386.

(14.) Chan ED, Kong P, Fennelly K, Dwyer AP, Iseman MD. Vertebral osteomyelitis due to infection with nontuberculous Mycobacterium species after blunt trauma to the back: Three examples of the principle of locus minoris resistentiac. Clin Infect Dis 2001;32:1506-1509.

(15.) Weiner BK, Love TW, Fraser RD. Mycobacterium avium-intracellulare: Vertebral osteomyelitis. J Spinal Disord 1998;11:89-91.

(16.) Horsburgh CR. Mycobacterium avium complex infection in the acquired immunodeficiency syndrome. N Engl J Med 1991;324:1332-1338.

(17.) Dutt AK, Stead VW. Long-term results of medical treatment in Mycobacterium intracellulare infection. Am J Med 1979;67:449-453.

(18.) Davidson PT, Khanijo V, Goble M, Moulding TS. Treatment of disease due to Mycobacterium intracellulare. Rev Infect Dis 1981;3:1052-1059.

(19.) Holland SM, Eisenstein EM, Kuhns DB, Turner ML, Fleisher TA, Strober W, et al. Treatment of refractory disseminated nontuberculous mycobacterial infection with interferon [gamma]: A preliminary report. N Engl J Med 1994;330:1348-1355.

(20.) Arend SM, Janssen R, Gosen JJ, Waanders H, de Boer T, Ottenhoff TH, et al. Multifocal osteomyclitis caused by nontuberculous mycobacteria in patients with a genetic defect of the interferon-[gamma] receptor. Neth J Med 2001;59:140-151.

RELATED ARTICLE: Key Points

* An elderly woman who had isolated skeletal involvement with MAI, mimicking Pott's disease, responded well to surgical excision of the inflamed tissue and antibiotic therapy.

* Mycobacterium avium-intracellulare (MAI) rarely causes disease of the spine in healthy individuals.

* Osteomyelitis due to MAL must be differentiated from that due to Mycobacterium tuberculosis because the treatment regimens are different.

Case Report

A 72-year-old white woman complained of a severe backache that had progressively worsened during a 2-week period. The pain was well localized to the area of the 12th thoracic vertebra and radiated to the lumbar region. She denied any fall or trauma. She denied cough or hemoptysis but felt as though she had a low-grade fever at night.

Her medical history included osteoporosis, polymyositis, congestive heart failure, and a compression fracture of the thoracolumbar vertebrae. Medications included 0.125 mg/d digoxin and 40 mg/d furosemide (every morning). The polymyositis was being treated with 10mg prednisone, which she had taken every other day for many years.

The patient was in moderate discomfort, but her vital signs were normal. She had tenderness to palpation in the lower thoracic spine. Bilateral muscle weakness was found in the lower extremities, and sensation to touch and pain was reduced in the ankles and soles. Deep tendon reflexes of the knees and ankles were diminished bilaterally. The remainder of the physical examination was unremarkable.

Results of complete blood cell count and metabolic panel were within the normal range. Her serologic test was negative for human immunodeficiency virus (HIV). The erythrocyte sedimentation rate (ESR) was 45 mm/h (West-ergren method). Chest x-rays were unremarkable. A destructive mass lesion involving the spine from T11 to L1 was recognized with magnetic resonance imaging. That imaging also indicated that a soft tissue extradural mass was compressing the anterior aspect of the spinal cord (Fig. 1).

Computed tomography-guided biopsy of the mass was obtained, and pathologic examination of the tissue indicated nonspecific inflammation. An open surgical biopsy of the spine was done to obtain a definitive diagnosis. This tissue contained multiple granulomas that were surrounded by epithelial cells and displayed central necrosis. There was no evidence of malignant cells. Acid-fast stain for mycobacteria was positive. A presumptive diagnosis of spinal tuberculosis (Pott's disease) was made and treatment was started with isoniazid, rifampin, and ethambutol in standard doses. An intermediate strength purified protein derivative (PPD) skin test showed no induration after 72 hours. A second intermediate strength PPD test 3 weeks later showed 5 mm of induration. After 3 weeks of antituberculous therapy, the patient's back pain improved slightly. The patient was transferred to a nursing home for convalescence and continued directly observed therapy.

The final culture reports from two separate samples obtained during the open excision biopsy identified MAI. None of the cultures grew Mycobacterium tuberculosis. Antibiotic therapy was modified. Isoniazid therapy was replaced with clarithromycin (500 mg twice a day), and rifampin and ethambutol were continued. Prednisone therapy was continued during the treatment of MAT disease. During the next few months, the patient's condition continued to improve. The back pain resolved, and sensory discrimination improved. Although a slight motor weakness persisted, she returned to her normal activity level.

From the Department of Internal Medicine, James H. Quillen College of Medicine, East Tennessee State University, Johnson City, TN. (Dr. Emery is with Pulmonary Associates of Kingsport, Kingsport, TN, and Dr. Girish is with Pulmonary Associates of East Tennessee, Johnson City, TN.)

Reprint requests to Jay B. Mehta, MD, Department of Internal Medicine, James H. Quillen College of Medicine, East Temessee State University, Box 70622, Johnson City, TN 37614-1709. Email: [e-mail]

Copyright [C] 2003 by The Southern Medical Association

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