—  SPECIALTY CONFERENCE  —

Pediatric Pathology

Case 4 - Kearns-Sayre Syndrome

Kathleen Patterson
Children's Hospital and Regional Medical Center and
University of Washington
Seattle, Washington


Click on each slide thumbnail image for an enlarged view
Clinical History:
16 year male with ptosis first noted in school photographs 5 years earlier. He was an otherwise healthy young man with a history of learning difficulties requiring special education. The ptosis persisted despite attempted surgical repair X 2. Ophthalmologic examination uncovered concomitant ophthalmoplegia and retinal pigment changes. Mitochondrial DNA studies on his blood were normal. The ophthalmologist then referred him to a geneticist who suggested a muscle biopsy to further evaluate his neuromuscular status.


Case 4 - Figure 1 - Trichrome stain; NADH.
Case 4 - Figure 2 - SDH; COX.
Case 4 - Figure 3 - Transmission electron microscopy (low and high magnification).

Mitochondrial Muscle Pathology

Case History:

Pathologic Findings

  • Light microscopy (frozen muscle):
    • Gomori trichrome – scattered ragged red fibers accounting for 3-5% of all myofibers; no endomysial fibrosis
    • Oxidative enzymes: Increased subsarcolemmal NADH and SDH staining scattered fibers; no increased vascular SDH staining; COX staining negative in 80% of fibers
    • Additional findings not included in photographs:
      • PAS - Increased glycogen in many fibers
      • ORO - coarse lipid droplets in increased numbers in many fibers
      • ATPase – 75% type 2 fiber predominance
  • Electron microscopy: Normally formed sarcomeres. Extensively abnormal mitochondria including concentric whorls and parallel packed arrays of cristae and paracrystalline inclusions

Differential Diagnosis
The ragged-red fibers (RRFs), and partial COX deficiency in light microscopy, and the mitochondrial paracrystalline inclusions noted on electron microscopic exam provide strong evidence for a mitochondrial myopathy. RRFs occur however in a spectrum of mitochondrial and non-mitochondrial disorders and do not point to a specific diagnosis (Table 1). The partial deficiency in COX staining, a finding indicative of respiratory chain complex IV malfunction, does little to narrow the differential. These findings combined with the clinical picture of chronic external ophthalmoplegia, ptosis, and retinitis pigmentosa are however virtually diagnostic of a limited spectrum of disorders including Kearns-Sayre syndrome and chronic external ophthalmoplegia (CPEO). Mitochondrial enzyme and DNA studies performed on snap frozen muscle tissue revealed low levels of respiratory chain complex I, III and IV activity and a 5 kb deletion of mitochondrial DNA to add confirmatory evidence for this diagnosis.

TABLE 1

Ragged Red Fibers
MitochondrialNon-Mitochondrial
KSS Myositis
CPEO Dystrophies
MERRF AZT Rx
MELAS Chronic Steroids
Pearson SyndromeAging

Diagnosis - Kearns-Sayre syndrome

Discussion
The clinicopathologic triad of ptosis, ophthalmoplegia, and ragged-red fiber myopathy identifies a group of disorders included under the rubric of CPEO syndromes1 (Table 2). Mitochondrial DNA deletions are frequently identified in these patients1,2; less commonly they may manifest mtDNA duplications or point mutations1. Of note, mitochondrial DNA deletions, unlike point mutations, are rarely detectable in blood samples.

TABLE 2

CPEO Syndromes
Kearns-SayreCPEO PlusCPEO
Onset <20 years
CPEO
Retinitis pigmentosa
One of following:
Complete heart block
CSF protein >100mg/dl
Cerebellar symptoms
Onset adolescent or young adult
CPEO
Retinitis pigmentosa
Extraocular symptoms variable
Lack KSS defining symptoms
Adult onset
CPEO only
Extraocular Manifestations
CardiacCNSEndocrine
Conduction defects
Cardiomyopathy		Cerebellar ataxia
Delayed development
Sensorineural Hearing Loss		Growth Failure
Diabetes Mellitus
Delayed puberty

The straightforward diagnosis rendered in this case is unfortunately not the norm for pediatric muscles biopsied to evaluate for mitochondrial myopathies. RRFs occur rarely in young children and COX enzyme negative fibers are minimally more common3,4. Less specific histologic features such as increased subsarcolemmal oxidative enzyme (NADH, SDH) staining, increased lipid and/or glycogen and type 1 or 2 fiber predominance may suggest a mitochondrial abnormality4, but are as likely to occur in other forms of muscle/metabolic disease. The histopathology of the muscle biopsy material may also be entirely normal4; in our own material 50% of cases with clinical and respiratory enzyme chain analysis evidence of a mitochondrial disorder displayed entirely normal muscle morphology. The histologic evaluation of muscle therefore may, if one is lucky, provide evidence to support a diagnosis of mitochondrial myopathy but absence of such finding cannot be used to exclude the diagnosis.

Electron microscopy has classically played a major role in the pathologic evaluation for mitochondrial disease with variety of ultrastructural changes described in mitochondrial disorders 5,6(Table 3). These ultrastructural changes are in fact identified in a higher number of suspected mitochondrial myopathy cases than are the light microscopic findings of RRFs and deficient COX staining4,7. Unfortunately these changes are not as specific as one would like and similar changes have been observed in muscular dystrophy, neurogenic atrophy, myositis and in otherwise seemingly normal muscle4. Ultrastructural findings therefore cannot be considered diagnostic of mitochondrial disorders but can severe as another piece of evidence in the quest for a firm diagnosis.

TABLE 3

Mitochondrial Ultrastructure
Increased numbers
Enlarged abnormally shaped
Sparse, concentric or bizarre cristae
Crystalloid (paracrystalline) inclusions

A major purpose of the muscle biopsy in these cases is to obtain analysis of the mitochondrial respiratory chain function and mtDNA. Although a finding of low respiratory chain enzyme activity seems as though it should lead to a straightforward diagnosis of a mitochondrial myopathy, the respiratory chain enzyme studies in reality aren't that straightforward. The most accurate and complete analysis requires study of the respiratory chain function of whole mitochondrial harvested from fresh muscle tissue8. This method is however possible only in a limited number of institutions and most muscle is studied after snap freezing in liquid nitrogen. Mitochondrial enzyme activity displays a wide range of normal values, but is rarely completely absent even in the face of significant defects3. Defining the border between normal and abnormal thus becomes an often arbitrary determination. Add to this a normally decreasing activity with age (e.g. 50% decrease in COX activity between 4 and 19 years9) combined with an inherent difficulty in obtaining age-matched normal control tissues. Finally factor in the variable handling muscle biopsy tissue undoubtedly receives during removal from the patient, snap freezing, and transporting to the specialty laboratory performing the testing and it is not hard to imagine how fraught with error the interpretation of mitochondrial enzyme analysis can become.

The study of mitochondrial DNA from blood or sampled uscle could add specificity to the diagnosis. Unfortunately only 10-20% of mitochondrial disorder in children are due to mtDNA mutations10,11. Increasing numbers of nuclear DNA mutations resulting in mitochondrial dysfunction are now being uncovered suggesting a potential for more readily availabe diagnostic studies in the near future.

Given all these uncertainties, how can one arrive confidently at a diagnosis of mitochondrial myopathy? A variety of diagnostic criteria, combining clinical, pathologic, mitochondrial enzyme analysis, and mtDNA data have been proposed to address this difficulty7,12-14. The United Mitochondrial Disease Foundation and allied groups ( www.mitosoc.org & www.mitoresearch.org) are currently working on creating consensus criteria for diagnosing mitochondrial disorders – watch those spaces.

References

  1. Shoffner JM. Mitochondrial myopathy diagnosis. Neurol Clin 2000;18(1):105-123.
  2. Moraes CT, DiMauro S, Zeviani M, et al. Mitodchondrial DNA deletions in progressive external ophthalmoplegia and Kearns-Sayre syndrome. NEJM 1989;320:1293-1299.
  3. Vogel H. Mitochondrial myopathies and the role of the pathologist in the molecular era. J Neuropathol Exp Neurol 2001;60(1):217-227.
  4. Rollins S, Prayson RA, McMahon JT, Cohen BH. Diagnostic yield of muscle biopsy in pateints with clinical evidence of mitochondrial cytopathy. Am J Clin Pathol 2001;116:326-330.
  5. Lindal S, Lund I, Torbergsen T, et al. Mitochondrial diseases and myopathies: a series of muscle biopsy specimens with ultrastructural changes in the mitochondria. Ultrastruc Pathol 1992;16:263-275.
  6. Kyriacou K, Mikellidou C, Hadjianastasiou A, et al. Ultrastructural diagnosis of mitochondrial encephatlomyopathies revisited. Ultrastruc Pathol 1999;23:163-170.
  7. Tulinius MH, Holme E, Kristiansson B, Larsson N-G, Oldfors A. Mitochondrial encephalomyopathies in childhood. I. Biochemical and morphologic investigations. J Pediatr 1991;119:242-50.
  8. Thorburn DR, Smeitink J. Diagnosis of mitochondrial disorders: clinical and biochemical approach. (Workshop report). J Inhert Meta Dis 2001;24:312-316.
  9. Lefai E, Terrier-Cayre A, Vincent A, et al. Enzymatic activities of mitochondrial respiratory complexes from children muscular biopsies. Age-related evolutions. Biochim Biop;hys Acta 1995;1228:43-50.
  10. Borchert A, Wolf NI, Wilichowski E. Current conceptgs of mitochondrial disorders in childhood. Sem Pediatr Neurol 2002;9:151-159.
  11. Smeitink J, van den Heuvel L, DiMauro S. The genetics and pathology of oxidative phosphorylation. Nat Rev Genet 2001;2:342-352.
  12. Walker UA, Collins S, Byrne E. Respiratory chain encephaloyopathies: a diagnostic classification. Eur Neurol 1996;36:260-267.
  13. Bernier FP, Boneh A, Dennett X, et al. Diagnostic criteria for respiratory chain disorder in adultgs and children. Neurol 2002;59:1406-1411
  14. Wolf NI, Smeitink JAM. Mitochondrial disorders. A proposal for consensus diagnositc criteria in infants and children. Neurol 2002;59:1402-1405.