June 18, 2021
Acquired Etiologies of Myopathy with Lobulated Muscle Fibers
An elderly male patient presents with a chief complaint of “dull achy pain.” The patient relates that the pain is predominantly in his thighs and hip girdle region, most intense in his left lateral thigh. He says the pain has ongoing and progressive for several months but has significantly worsened over the last few days. The patient had been recently admitted for “rhabdomyolysis” thought due to his statin medication, which was discontinued; however, no muscle biopsy was performed at that time and his muscle enzymes showed CPK 934. Other past medical history includes diabetes mellitus, hyperlipidemia, hypertension, hypercalcemia, and vitamin D deficiency. Physical exam shows preservation of muscle strength and no skin rash. Due to clinical concern for a possible acquired inflammatory myopathy, such as polymyositis, the decision was made to biopsy the left thigh. The muscle biopsy shows lobulated muscle fibers, see Figure 1 and Figure 2.
What are a few of the acquired etiologies for myopathy with lobulated muscle fibers?
Myopathy with lobulated muscle fibers in an elderly male presenting with myalgias. Two photomicrographs are shown of snap frozen skeletal muscle stained with the Modified Gomori Trichrome (MGT) preparation demonstrating variably sized variably well-developed muscle fibers with irregular basement membrane contours and myofibrillar disorganization due to small triangular or wedge-shaped subsarcoplasmic areas of fuchsinophilic/red staining character, consistent with small accumulations of mitochondria (also known as so-called “lobulated muscle fibers”). Some of the lobulated muscle fibers are in small groups (Figure 1) or scattered as single individual myofibers throughout the specimen. Original magnifications: Figure 1 MGT, 200x; and Figure 2 MGT, 400x.
Answer: All of the Above
If you chose answer choice (D), all of the above, then you’re correct! Lobulated (trabeculated) muscle fibers are not entirely specific as to etiology and may be seen in acquired conditions such as hypothyroidism (thyroid-related myopathy), inflammatory conditions (broad category), as well as toxic conditions, such as alcohol-related myopathy. See references below.
Other conditions include osteomalacia and even sometimes denervation-type changes. Of note, denervation-type changes can show a number of nonspecific changes, even ring fibers. Much has been written about lobulated fibers in various entities, and their etiology is believed to stem from anchoring defects of harboring mitochondria in locations near the Z-disc. Lobulated muscle fibers are typically 1 type myofibers.
A proper commentary on lobulated muscle fibers would be remiss if it were too not at least mention the other more classical associations of lobulated muscle fibers. As stated previously, lobulated muscle fibers are not entirely specific to one clear-cut defined myopathic process; however, there is an associated with calpainopathy – that is to say, limb-girdle muscular dystrophy associated with calpain-3 deficiency (LGMD 2A), which is an autosomal recessive disease. Lobulated muscle fibers have also been described in other myopathic processes, such as facioscapulohumeral dystrophy (FSHD), spinal muscle atrophy (SMA), and congenital muscular dystrophy (CMD).
Burns DK, et al. Skeletal Muscle Biopsy Evaluation. A Case-Based Guide to Neuromuscular Pathology, 2020: 3-48.
Figarella-Branger D, El-Dassouki M, Saenz A, et al. Myopathy with lobulated muscle fibers: evidence for heterogeneous etiology and clinical presentation. Neuromuscul Disord. 2002 Jan;12(1):4-12. PMID: 11731278.
Guerard MJ, Sewry CA, Dubowitz V. Lobulated fibers in neuromuscular diseases. J Neurol Sci. 1985 Jul;69(3):345-56. PMID: 3162002.
Tsuburaya R, et al. Lobulated fibers in a patient with 46-year history of limb-girdle muscle weakness. Neuropathology. 2011;31:455-7.
Weller B, Carpenter S, Lochmüller H, Karpati G. Myopathy with trabecular muscle fibers. Neuromuscul Disord. 1999 Jun;9(4):208-14. PMID: 10399746.