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Myopathy

Characteristic MRI Muscle Involvement Patterns

Dermatomyositis (DM)

Symmetric edema and fatty infiltration in proximal muscles of the pelvic and shoulder girdles (thigh and upper arm muscles). MRI often shows a “honeycomb” reticular pattern of intramuscular edema with peripheral subfascial distribution, and frequent high signal in fascia and subcutaneous tissue (distinguishing DM). Neck flexors and paraspinals may be involved in severe cases.

Polymyositis (PM)

Similar to DM, with symmetric proximal limb muscle involvement (thighs, hip and shoulder girdle) on MRI. Lacks the distinctive DM-specific peripheral reticular edema pattern – instead showing more uniform muscle edema. Fascia or subcutaneous edema is less prominent than in DM. (PM is essentially a diagnosis of exclusion with no unique MRI hallmarks beyond diffuse proximal myositis.)

Inclusion Body Myositis (IBM)

Selective involvement: Marked fatty atrophy of the quadriceps (especially distal vastus intermedius and medialis), while the rectus femoris is relatively spared. Anterior thigh and distal thigh muscles show the most fatty replacement. In the legs, the gastrocnemius is prominently affected with relative sparing of the tibialis posterior and soleus muscles. In upper limbs, the deep finger flexor (flexor digitorum profundus) is characteristically involved. Pelvic girdle (gluteal) muscles are less involved than thighs. This pattern (fatty fibrous infiltration of both distal quadriceps) has ~80% sensitivity and 100% specificity for IBM.

Immune-Mediated Necrotizing Myopathy (IMNM)

Predominantly affects thigh and pelvic muscles on MRI, reflecting severe lower limb weakness. MRI shows more extensive edema in the thigh muscles than seen in DM/PM. There is also greater fatty replacement/atrophy in IMNM, especially involving the gluteal muscles and lateral hip rotators. (This correlates with the clinical pattern of marked proximal lower limb weakness in IMNM.)

Antisynthetase Syndrome Myositis (ASyS)

MRI pattern overlaps with DM/PM but with prominent fasciitis. Along with thigh muscle edema, ASyS patients frequently show high T2 signal and thickening in muscle fascia and intermuscular septa. This fascia involvement on MRI is a hallmark in antisynthetase syndrome (often with concurrent interstitial lung disease clinically). Muscle edema is generally symmetric and proximal, similar to other inflammatory myopathies.

Duchenne Muscular Dystrophy (DMD)

Distinctive “trefoil” pattern in thighs: relative sparing of the gracilis, sartorius, and adductor longus muscles, plus semitendinosus (“single fruit”), while other thigh muscles (quadriceps, adductor magnus, hamstrings) show early fatty replacement. Pelvis and thigh muscles are severely affected even in early stages, whereas lower leg muscles are comparatively less involved until later. The gluteal muscles and adductor magnus are preferentially involved early, and the quadriceps and biceps femoris become fatty replaced in later stages. In the legs, the gastrocnemius and peroneus longus are most affected, while the tibialis anterior (anterior compartment) remains relatively spared until advanced disease. The gracilis, sartorius, and semimembranosus remain remarkably resistant to fat infiltration until late. Calf muscles often exhibit pseudohypertrophy (enlarged by fat).

Becker Muscular Dystrophy (BMD)

MRI pattern resembles DMD but milder/slower. Preferential early fatty infiltration of the gluteals and adductor magnus, with relative sparing of the sartorius and gracilis. Thigh “trefoil” sparing (gracilis, sartorius, adductor longus) is often present as in DMD. Quadriceps and biceps femoris involvement occurs later in disease. (Rarely, a “quadriceps-sparing” phenotype of BMD is observed – an atypical variant with disproportionate preservation of quadriceps muscle bulk.)

Sarcoglycanopathy (LGMD2C-2F)

Pattern resembles dystrophinopathy. Marked fatty degeneration in pelvic and thigh muscles with a DMD-like sparing of medial thigh muscles in some cases. For example, a “single fruit” sign (spared semitendinosus) with gracilis/sartorius sparing can occur, but less consistently than in DMD. Some patients show a “concentric” pattern of thigh muscle fatty infiltration (selective involvement of vastus intermedius/medialis with relative sparing of vastus lateralis and rectus femoris). Lower legs typically show relative sparing of tibialis posterior and other deep muscles, with gastrocnemius more affected. Overall, fatty infiltration is severe in thighs/pelvis and milder in calves.

Calpainopathy (LGMD R1, LGMD2A)

Selective thigh involvement on MRI: commonly the adductor magnus and posterior thigh muscles are heavily infiltrated, while the anterior thigh muscles (e.g. rectus femoris) and certain medial muscles (adductor longus, gracilis) are relatively spared. This can produce an “hourglass” appearance on thigh cross-sections. The sartorius may be involved (unlike many dystrophies). In calves, the soleus is often more affected than gastrocnemius, and the peroneal (lateral leg) muscles more than the tibialis anterior. Early involvement of gluteus minimus and paraspinals has also been reported.

Dysferlinopathy (LGMD R2, LGMD2B / Miyoshi)

Posterior compartment pattern: pronounced fatty replacement in the hamstrings and gastrocnemius/soleus muscles, with relative sparing of quadriceps and anterior leg compartment. Many patients exhibit the “diamond on quadriceps” sign on MRI – a patch of fatty infiltration centrally in the rectus femoris with preserved muscle rim, seen in ~2/3 of dysferlinopathies. The sartorius is often involved (notably, since it is spared in most other LGMDs). The pattern can vary, but generally the calf muscles (especially soleus) and posterior thighs degenerate early, while hip adductors and anterior tibial muscles are relatively preserved until later.

FKRP-Related LGMD (LGMD2I)

MRI often shows a “concentric fatty infiltration” pattern in the thighs that is highly specific for FKRP dystroglycanopathy. This appears as preferential fatty replacement of the central parts of quadriceps (vastus intermedius/medialis) with a rim of preserved muscle (vastus lateralis and rectus femoris). Marked involvement of posterior thigh and gluteal muscles is also seen. Lower legs usually have relatively mild changes early on, with tibialis posterior and flexor muscles often spared until later. Overall, thigh and pelvic muscles are more severely involved than calves.

Facioscapulohumeral Dystrophy (FSHD)

Characteristic asymmetric shoulder girdle involvement. MRI shows early fatty infiltration of the trapezius (upper back) in nearly all patients and the serratus anterior (~85% of patients), reflecting scapular winging. The pectoral and biceps/triceps muscles often become involved, while the deltoids are relatively spared until later. As disease progresses, there is involvement of abdominal muscles (especially lower rectus abdominis) and paraspinals, contributing to lumbar lordosis. Lower limb involvement is variable – foot dorsiflexors (tibialis anterior) may be affected leading to foot drop, and some distal leg muscles can be involved in advanced FSHD – but thigh muscles are often spared or only mildly affected compared to the shoulder girdle.

Emery–Dreifuss Muscular Dystrophy (EDMD)

Humero-peroneal pattern on MRI. Early selective fatty changes in the upper arms (biceps and triceps brachii) with preserved deltoids. In the lower legs, early involvement of the anterior compartment (tibialis anterior, extensor digitorum longus) and peroneal muscles is common. The calf (gastrocnemius) and thigh muscles may be less severely affected in early stages, though vastus lateralis and gluteus muscles can show changes over time. The overall pattern is a combination of shoulder/upper arm weakness and distal leg (peroneal) weakness, with relative sparing of hip abductors and often the deltoid. Elbow and Achilles tendon contractures correspond to early selective muscle involvement.

Oculopharyngeal Muscular Dystrophy (OPMD)

Primarily affects cranial muscles (not visible on limb MRI). On skeletal muscle MRI, proximal limb muscles can show mild to moderate fatty infiltration in long-standing disease. Thigh muscles – especially the hip adductors and hamstrings – are reported to be involved in many OPMD patients. For example, MRI often shows fatty changes in the adductor magnus and semimembranosus. The shoulder girdle may also be mildly affected (e.g. biceps) in late stages. (Overall MRI changes are less pronounced than in limb-girdle dystrophies, and may precede overt weakness.)

Collagen VI Myopathy (Ullrich/Bethlem)

Distinct “striped” pattern on thigh MRI. There is often a peripheral rim of fatty infiltration in muscles like the vastus lateralis with a central area of preserved muscle (“central shadow” or target appearance). Multiple alternating streaks of normal and replaced tissue (a “tiger stripe” appearance) are highly specific for COL6-related myopathies. In Ullrich (severe), fatty changes are diffuse but still spare the sartorius, gracilis, and adductor longus relative to other thigh muscles. In calves, involvement of gastrocnemius with relative sparing of tibialis anterior can be seen. Early contractures around ankles and elbows correspond to selective muscle involvement.

Merosin-Deficient Congenital Dystrophy (LAMA2)

Diffuse early involvement of nearly all limb muscles on MRI. There is little to no selective sparing of individual muscles – most thigh and calf muscles show severe fatty replacement from infancy. (This contrasts with other dystrophies where sartorius/gracilis may be spared – in merosin deficiency, even those are involved.) The pattern is a generalized and advanced muscle degeneration in pelvic, thigh, and calf compartments. Occasionally the tibialis anterior and forearm flexors remain functional slightly longer, but MRI in classic LAMA2-CMD shows a near-complete fatty infiltration of proximal and distal muscles.

Nemaline Myopathy (NEB/ACTA1)

MRI patterns vary by genetic subtype. NEB (Nebulin)-related nemaline myopathy can show selective distal involvement: in mild cases, tibialis anterior and soleus are selectively fatty while thigh muscles are completely spared. In more moderate nebulin-NM, there is predominant fatty involvement of the rectus femoris, vastus lateralis, and hamstrings, with diffuse involvement of the anterior leg compartment and soleus. ACTA1 (alpha-actin) nemaline myopathy tends to cause diffuse fatty infiltration of both thigh and leg muscles, with relative sparing of the gastrocnemius muscles. These selective patterns can help distinguish nemaline myopathy subtypes from other congenital myopathies.

Centronuclear Myopathy (X-linked MTM1)

Diffuse, severe involvement of nearly all skeletal muscles from infancy. MRI in X-linked myotubular myopathy typically shows homogeneous fatty replacement of the thigh, pelvic, and paraspinal muscles early in life (consistent with profound weakness). There is no clear regional sparing – quadriceps, hamstrings, gluteals, and calves are all severely affected. Some surviving patients exhibit pseudohypertrophy of the calves; MRI reveals that to be fatty infiltration. (Overall, XL-CNM shows a non-selective severe pattern on MRI due to its diffuse nature.)

Centronuclear Myopathy (AD DNM2)

Distal predominance on MRI. Dynamin-2 related CNM often shows prominent fatty involvement of the lower leg muscles – particularly the soleus, as well as gastrocnemius and tibialis anterior. Thigh muscles may be less affected early, though some patients have adductor magnus and semitendinosus involvement. Calf atrophy (with soleus very affected) and foot drop (from tib anterior involvement) are common features on imaging. Paraspinal muscles can also show fatty changes in DNM2-CNM.

Central Core Disease (RYR1-related)

MRI often shows selective involvement of proximal muscles. A common pattern in dominant RYR1 myopathy is fatty infiltration of the hip adductors and gluteus muscles, with relative sparing of the thigh anterior compartment (quadriceps) in early stages. Calf muscles may also be involved in a “patchy” pattern. In some RYR1 cases, a “selective panvastus” pattern is noted – preferential vastus medialis/lateralis involvement. Multiminicore disease (recessive RYR1) can show more diffuse changes. (Overall, RYR1 MRI patterns are variable but often point to hip and thigh muscle involvement with certain muscles spared, helping identify RYR1 mutations.)

Myofibrillar Myopathies (MFM)

Different MFMs have distinct patterns. Desmin-related myopathy MRI often shows early severe fatty changes in the distal legs (gastrocnemius-soleus complex and peroneal muscles) and selective involvement of some thigh muscles (e.g. semitendinosus, sartorius, gracilis) with relative sparing of others. In contrast, myotilinopathies and filamin-C myopathy tend to preferentially involve the biceps femoris, adductor magnus, and semimembranosus in the thighs. A “sandwich” or peripheral rim of thigh muscle involvement has been described in some MFMs. Many myofibrillar myopathies also show prominent paraspinal muscle fatty replacement and asymmetrical calf involvement. The presence of a distinctive pattern (e.g., combined proximal and distal involvement with certain muscles spared) on MRI can guide genetic diagnosis.

GNE Myopathy (HIBM)

A “quadriceps-sparing” distal myopathy. MRI reveals severe fatty degeneration in the anterior lower leg muscles, especially the tibialis anterior, with relative preservation of the quadriceps even in advanced disease. The hallmark is early foot drop (tibialis anterior replaced by fat) while the thigh muscles (notably quadriceps) remain intact until late. Posterior calves (gastrocnemii) and hamstrings can also be involved as the disease progresses, but the sparing of quadriceps is distinctive. This selective pattern differentiates GNE myopathy from other inclusion-body myopathies.

Metabolic Myopathy – Pompe Disease

Paraspinal and proximal limb involvement. MRI in late-onset Pompe often shows early fatty infiltration of the paraspinal (erector spinae) muscles, sometimes even in presymptomatic individuals. The thigh and pelvic girdle muscles (hip flexors, adductors, quadriceps) become involved next, leading to a limb-girdle pattern. The diaphragm (not typically imaged on limb MRI) and abdominal muscles are also frequently affected, correlating with respiratory weakness. In the lower legs, Pompe can show moderate involvement of gastrocnemius and soleus, but the axial muscles (paraspinals) are disproportionately affected on imaging. Scapular stabilizers may show fatty change, explaining winged scapula in Pompe.

Metabolic Myopathy – McArdle (GSD V)

Selective pattern involving paraspinal and scapular muscles. Whole-body MRI in McArdle disease reveals that the paravertebral muscles (especially the deep rotatores and semispinalis) are prominently affected, with relative sparing of the multifidus. The erector spinae (longissimus, iliocostalis) show marked fatty replacement, whereas the psoas and quadratus lumborum are notably spared. In the shoulder girdle, the subscapularis and serratus anterior often have fatty changes. Thigh muscles may show patchy involvement (e.g., adductor longus or quadratus femoris in some cases) with asymmetry. Calf involvement is usually mild until late; some advanced cases show calf muscle infiltration. This pattern – paraspinal and certain shoulder muscle involvement with sparing of hip flexors – is characteristic for McArdle’s disease on MRI.

Metabolic Myopathy – CPT2 Deficiency

Patchy, asymmetric involvement with quadriceps sparing. In the adult myopathic form of CPT II deficiency, MRI often shows essentially normal quadriceps muscles with fatty changes primarily in other thigh muscles. Fat infiltration can be patchy and asymmetric in the hamstrings and calf muscles, reflecting episodic rhabdomyolysis injury. The posterior thigh and calf (e.g. soleus, gastrocnemius) might show mild chronic changes, and sometimes the peroneal group is affected. Overall, a relative sparing of the quadriceps combined with uneven thigh/calf involvement is suggestive of CPT2 myopathy (especially in context of exercise-induced myoglobinuria).

Neutral Lipid Storage Myopathy (NLSD)

Diffuse fatty infiltration with some selective shoulder involvement. Whole-body MRI in neutral lipid storage disease with myopathy (e.g. PNPLA2 mutation) shows widespread muscle fat replacement in proximal limbs. Commonly, the shoulder girdle muscles – notably supraspinatus and infraspinatus – are atrophic on MRI. Thigh and calf muscles are diffusely involved, often resembling a limb-girdle dystrophy pattern (both pelvic and shoulder muscles affected). No single muscle is uniquely spared, though mild asymmetry can occur. The MRI appearance is one of a generalized myopathy with dystrophic changes (fatty replacement in many muscle groups). This pattern, along with vacuolar histology, helps identify NLSD-M.

Mitochondrial Myopathies

Generalized or patchy symmetric involvement. Many primary mitochondrial myopathies (e.g. MELAS, Kearns-Sayre syndrome) show a fairly diffuse pattern of muscle involvement on MRI, often affecting proximal muscles in a symmetric fashion. However, certain subtypes have clues: for instance, TK2 deficiency (a mitochondrial DNA maintenance disorder) has a specific lower limb MRI pattern with selective involvement (reported as unique among mitochondrial myopathies). In some mitochondrial myopathies, MRI can show selective calf muscle or anterior compartment involvement mimicking LGMD. Generally, though, mitochondrial myopathy MRI is not highly specific – it may reveal global fatty atrophy in thighs and calves with no clear sparing pattern. One exception is GDF15-related mitochondrial myopathy which can have patchy thigh involvement. (Overall, MRI serves more to confirm the presence of myopathic changes in suspected mitochondrial cases rather than a distinct pattern.)