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Targetoid muscle fibers are a type of muscle fiber that can be observed in patients with paralysis of the deltoid and supraspinatus muscles. They are characterised by round lesions consisting of at least three concentric zones: a central disk, a peripheral pale ring, and an erythematous halo. These targetoid fibers are typically found in muscle biopsies and studied using light and electron microscopy. The probable cause of the associated neuropathy is tumor compression. Targetoid fibers are associated with neurogenic muscular atrophy and can be observed in conditions such as dermatophyte infections, granuloma annulare, and Lyme disease. They are also linked to changes in innervation and re-innervation of muscle fibers.
| Characteristics | Values |
|---|---|
| Definition | Targetoid muscle fibers are a type of change observed in muscle biopsies from patients with paralysis of the deltoid and supraspinatus muscles. |
| Cause | Tumor compression |
| Occurrence | Targetoid changes are confined to hypertrophic or normal-sized fibers. |
| Microscopic Appearance | Up to 4 structural zones can be seen in target fibers, but many lack zone 2 (halo) or zone 3. |
| Formation | Focal irregularity and streaming of Z-bands are thought to be primary alterations in the formation of targetoid fibers. |
| Induction | Partial residual innervation and re-innervation induce the formation of targetoid fibers. |
| Associated Disorders | Dermatophyte infections, granuloma annulare, reactive conditions, Lyme disease, leprosy. |
| Lesion Characteristics | Regular, well-defined round papules or plaques with at least three concentric zones: a central disk, peripheral pale ring, and an erythematous halo. |
| Diameter | Lesions typically measure less than 3 cm in diameter. |
| Symptoms | Lesions are generally asymptomatic but may cause burning or itching sensations. |
| Healing | Lesions heal without scarring. |
| NADH-TR and SDH Activity | Higher activity is observed in type 1 fibers compared to type 2 fibers. |
| Innervation Issues | Changes in fiber types can indicate issues with innervation and re-innervation of muscle fibers. |
| Atrophic Fiber Distribution | The shape and distribution of atrophic fibers can provide clues about the underlying etiology. |
| Histochemical Analysis | Provides insights into the internal structure and abnormalities within muscle fibers. |
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What You'll Learn
- Tumour compression as a probable cause of neuropathy
- Targetoid fibres appear in cases of acute or subacute denervation
- Targetoid fibres are found in type-1 muscle fibres
- Targetoid lesions are distinct clinical configurations that include dermatophyte infections, granuloma annulare, and reactive conditions
- Targetoid fibres are studied through light and electron microscopy
Tumour compression as a probable cause of neuropathy
Target and targetoid fibres are a phenomenon observed in human muscle fibres. A study by Yagishita et al. in 1977 examined target and targetoid fibres in a muscle biopsy from a patient with paralysis of the deltoid and supraspinatus muscles. The probable cause of the neuropathy was tumour compression.
Tumour compression is a probable cause of neuropathy, specifically in the case of target and targetoid fibres. Tumours can cause nerve compression, leading to typical compression symptoms or even persistence or recurrence after surgery. The median nerve, for example, can be compressed by a tumour, resulting in carpal tunnel syndrome (CTS). CTS is the most common site of median nerve compression, but other proximal compressions such as pronator syndrome and Lacertus syndrome can also occur. The most common published cause of median nerve compression is lipofibromatous hamartoma (LFH), but lipomas, ganglion cysts, and fibromas have also been found in the trajectory of the median nerve. These tumours can be challenging to diagnose due to their uncommon presentation of symptoms, which may result in a prolonged diagnostic process or multiple surgical procedures.
In the study by Yagishita et al., target and targetoid changes were observed exclusively in hypertrophic or normal-sized fibres. A morphometric evaluation of these fibres showed no significant difference between them. However, when viewed under an electron microscope, up to four structural zones were visible in the typical target fibre, while many were missing either zone 2 (halo) or zone 3, or both.
The target-targetoid phenomenon in muscle fibres is associated with impaired innervation, specifically partial residual innervation and re-innervation. This phenomenon can be studied through histological, histochemical, and ultrastructural analyses, providing insights into the relationship between target, targetoid, and targetoid/core fibres in severe neurogenic muscular atrophy.
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Targetoid fibres appear in cases of acute or subacute denervation
Targetoid muscle fibres are a type of muscle fibre that can be observed in patients with paralysis of the deltoid and supraspinatus muscles. They are characterised by well-defined round papules or plaques consisting of at least three concentric zones: a central disk, a peripheral pale ring, and an erythematous halo. The appearance of targetoid fibres is indicative of impaired innervation and is associated with neuropathic conditions.
The presence of targetoid fibres can be studied through muscle biopsies and visualised using light and electron microscopy. In a study by Yagishita et al. (1977), target and targetoid fibres were observed in a patient with paralysis caused by tumour compression. The changes in the muscle fibres were confined to hypertrophic or normal-sized fibres. Through electron microscopy, up to four structural zones were identified in the typical target fibre, but some fibres lacked zone 2 (halo) or zone 3, or both.
The formation of targetoid fibres is believed to be associated with focal irregularity and streaming of Z-bands, which may be induced by partial residual innervation and re-innervation. This suggests that targetoid fibres are a result of impaired nerve function or damage.
Targetoid fibres have been observed in cases of acute or subacute denervation, which refers to the damage or degeneration of nerve cells that supply the muscle. Denervation can be detected through needle EMG, which reveals abnormal spontaneous activity in the affected muscles. This includes the presence of fibrillation potentials and positive sharp waves, indicating hypersensitivity of the denervated muscle fibres to acetylcholine.
Additionally, MRI is a valuable tool for detecting denervated muscles, especially in cases of brachial and lumbosacral plexopathies. Acute denervation may not show any imaging abnormalities initially, but after approximately two weeks, there is an increased muscle signal on T2-weighted and inversion-recovery sequences. Subacute denervation, on the other hand, is characterised by T2 prolongation and postcontrast enhancement, indicating early changes in the muscles.
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Targetoid fibres are found in type-1 muscle fibres
Targetoid muscle fibres are a type of muscle fibre associated with impaired innervation. They are found in type-1 muscle fibres, which are also known as slow oxidative (SO) fibres. These fibres contract relatively slowly and use aerobic respiration (oxygen and glucose) to produce ATP.
The target-targetoid phenomenon in human muscle fibres has been studied using light and electron microscopy. These studies have observed that target and targetoid changes occur exclusively in hypertrophic or normal-sized fibres. While target fibres typically exhibit up to four structural zones, targetoid fibres often lack zone 2 (halo) or zone 3, or both. This distinction is important in understanding the underlying pathology associated with these fibres.
The formation of targetoid fibres is believed to be induced by partial residual innervation and re-innervation, resulting in focal irregularity and streaming of Z-bands. These fibres are often observed in muscle biopsies from patients with paralysis of the deltoid and supraspinatus muscles, with the probable cause being tumour compression. Additionally, targetoid fibres are associated with neurogenic muscular atrophy and may exhibit a clear difference in diameters compared to non-atrophic muscle fibres.
Targetoid fibres are also characterised by their round contour, increased number of internal nuclei, and variability in fibre diameter. They are typically found in an even distribution, ranging from small to normal-diameter fibres. The study of targetoid muscle fibres provides valuable insights into muscle function, innervation, and various pathological conditions.
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Targetoid lesions are distinct clinical configurations that include dermatophyte infections, granuloma annulare, and reactive conditions
Targetoid lesions are distinct clinical configurations that include dermatophyte infections, granuloma annulare, and various reactive conditions. They are characterised by acute targetoid erythematous lesions with a symmetric, acral distribution. Targetoid lesions are typically regular, well-defined round papules or plaques consisting of at least three concentric zones: a central disk, a peripheral pale ring, and an erythematous halo. They are generally asymptomatic, although some patients may report burning or itching sensations. These lesions persist for one week or longer and heal without scarring.
Dermatophyte infections are usually acquired from other humans or other sources, such as animals or the environment. They typically present with annular lesions, commonly known as "ringworm," when they affect glabrous skin areas such as the face, groin, and trunk. Granuloma annulare, on the other hand, typically lacks appreciable scale and can be chronic in nature.
Various reactive conditions can also manifest as targetoid lesions. For example, erythema migrans and erythema multiforme are typically acute disorders, with erythema multiforme often characterised by target lesions. These target lesions have a distinctive appearance, often referred to as "bulls-eye" or "cockade" lesions due to their concentric rings. They can appear on various body sites, including the face, upper chest, back, arms, and legs.
In addition to these common disorders, targetoid lesions can also be associated with more serious diseases, such as Lyme disease and leprosy. A thorough medical history, including travel history, and diagnostic techniques such as skin biopsies, are important tools in distinguishing between these various conditions.
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Targetoid fibres are studied through light and electron microscopy
With light and electron microscopy, it was observed that target and targetoid changes were confined to hypertrophic or normal-sized fibres. There was no significant difference between the target and targetoid fibres. However, with an electron microscope, up to four structural zones were observed in the typical target fibre. Many target fibres were also observed to be devoid of either zone 2 (halo) or zone 3, or both.
The study of these target and targetoid fibres through light and electron microscopy has provided valuable insights into the nature of these fibres and their relationship to neurological conditions. The use of microscopy has allowed researchers to identify the presence of concentric zones within the fibres, which has informed our understanding of their structure and potential pathogenic features.
Furthermore, the use of light and electron microscopy in the study of targetoid fibres has contributed to our understanding of the underlying causes and mechanisms of targetoid fibre formation. It has been suggested that focal irregularity and streaming of Z-bands are the primary alterations in the formation of these fibres, induced by partial residual innervation and re-innervation.
Overall, the application of light and electron microscopy in the study of targetoid fibres has been instrumental in advancing our knowledge of these unique muscle fibres and their role in various neurological and muscular conditions.
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Frequently asked questions
Targetoid muscle fibres are associated with neuropathy, and are typically found in patients with paralysis of the deltoid and supraspinatus muscles. They are usually identified by light and electron microscopy.
Target fibres are round areas with lower activity of NADH-tetrazolium reductase, an enzyme mainly located at mitochondria, seen in the centre or the epicentre of muscle fibres. Targetoid fibres, on the other hand, do not have a clear margin.
The probable cause of neuropathy in patients with target and targetoid fibres is tumour compression. The changes in the fibres are confined to hypertrophic or normal-sized fibres.
