Diagnostic criteria are used to establish a diagnosis of IIM (“myositis”), (including JDM and IBM). In general, these sets of criteria are developed on a basis of consensus and are subject to change over time due to expanding knowledge. Clinical features, laboratory features, and histopathological findings play a key role within these diagnostic criteria. IIM, JDM or IBM can present itself in numerous ways. The sum of symptoms and signs, and the results of ancillary investigations make a diagnosis likely or less likely, but one feature may outweigh the other or may predict a specific clinical subtype.

In the previous guideline, typical skin abnormalities were mentioned as a criterium for dermatomyositis (DM). Lately it has become clear that dermatomyositis-like skin lesions can be present in immune-mediated necrotizing myopathy, although this is rare. In addition, skin lesions can also be present in overlap myositis (OM) as part of the connective tissue disease and in the anti-synthetase syndrome. A revision to clinically recognize the subtype accurately is therefore warranted. Here, we describe symptoms and signs, including patterns of muscle weakness, with a high predictive value for a specific subtype of IIM. The recognition of these symptoms and signs aids the physician to speed up the diagnostic trajectory, to start treatment earlier, and to monitor the clinical course. An attempt will be made to highlight the distinguishing features.

Characteristics of skeletal muscles

Common patterns of muscle weakness at presentation:

• Subacute, more or less symmetrical proximal lower and/or upper limb girdle muscle weakness which evolves in weeks to months, is a frequent first sign of IIM, except IBM. The main complaints are difficulty to reach above shoulder height, unstable gait, and difficulty walking stairs without support, or difficulty rising from a chair.
• If weakness is foremost present in the lower extremities compared with the upper extremities, this can point towards immune-mediated necrotizing myopathy (IMNM), as that is the predominant clinical picture in that subtype of idiopathic inflammatory myopathy (IIM) (Allenbach, 2020).
• In IBM, slowly progressive muscle weakness which takes more than 6 months to evolve and to become clinically relevant, especially when there is a debut in the quadriceps (figure 1) or deep finger flexors (figure 2). The main symptoms and signs are problems with rising from a chair, falls, and diminished hand grip strength. Weakness is usually asymmetric, and atrophy of the afflicted muscles can be seen (Rose, 2013).
• Weakness of oropharyngeal muscles can be present in IIM, including JDM and IBM and can result in dysphagia, which may be the first presenting symptom of IIM. A feeling of obstruction or aspiration while swallowing (especially food) are the usual complaints.

Figure 1. Atrophy of the quadriceps muscles in IBM.

Uncommon, but recognizable patterns of muscle weakness at presentation:

• Slowly progressive, more or less symmetrical proximal weakness of arms and legs, which evolves over more than 6 months is a rare presentation for IIM, mimicking a limb-girdle muscular dystrophy, but has been described in IMNM with HMGCR antibodies and SRP antibodies (Allenbach, 2020). Some of these patients may show scapular winging.
• Axial weakness (a dropped head or camptocormia) can be present in IIM, including IBM.
• Distal weakness of the legs leading to a drop foot, mimicking (asymmetric) motor neuropathy, can be the presenting sign in IBM. Atrophy is often apparent.
• Respiratory weakness can be the first presentation of IBM in rare cases (Voermans, 2004).

Figure 2. Asymmetric weakness in IBM of the deep finger flexors, with inability to disguise the fingernails during maximal effort to make a fist.

Unusual signs:

• Predominating weakness of facial muscles at the beginning of the disease should prompt a different diagnosis and not IIM, JDM or IBM. IBM patients can have prominent symmetrical facial weakness in a later stage of the disease, especially of eye-closure. Usually, the weakness in the face remains mild in IBM.
• External eye muscle weakness or orbital myositis is not a feature in the early stages of the abovementioned forms of inflammatory myopathies, although it has been coined as part of the spectrum of immune-checkpoint inhibitor associated myositis.

No weakness

Dermatomyositis (DM) and JDM can present without clinically noticeable involvement of skeletal muscles, usually referred to as clinically amyopathic dermatomyositis (CADM). More precisely, it is called hypomyopathic when there is no weakness but ancillary investigations point towards muscle involvement, and amyopathic when ancillary investigations do not show muscle involvement either. Up to 20% of DM patients have CADM. In IBM, clinically observable weakness of skeletal muscles is a requirement for the diagnosis.

Characteristics of the skin

Skin changes can be present in DM, JDM, the anti-synthetase syndrome, overlap myositis and IMNM. Skin involvement is not an obvious feature in IBM.

Skin changes in dermatomyositis

According to the literature, skin changes can be either pathognomonic, characteristic, compatible, less common or nonspecific. As there is doubt as to whether these so-called pathognomonic skin changes are really pathognomonic, the workgroup decided to avoid this terminology and to divide the skin lesions into highly suggestive for the disease or those compatible with the diagnosis based on frequency of occurrence. The predominant abnormal feature of the skin is erythema. Other common findings are edema and hyperkeratotic changes. For the elaboration below, several articles have been used (Czirjak, 2014; DeWane, 2019; Didona, 2020; Bogdanov, 2018; Tanimoto, 1995; Mainetti, 2017; Mammen, 2020).

Most common skin abnormalities at presentation, highly suggestive for dermatomyositis:

• Gottron’s papules^{*$&@#^}: Violaceous or purplish slightly elevated lesions and plaques, overlying the metacarpophalangeal, proximal and distal interphalangeal joints of the hands, sometimes with subtle scale. Figure 3. There is an erythematous background over the bony prominences. Depigmentation, atrophy and scaring can be present when lesions resolve.
• Gottron’s sign^{*&@#^:} Erythematous macules or patches in a linear arrangement over extensor surfaces of the hands and the elbows, knees, and ankles. Slight scale may be present.
• Heliotrope rash^{*&$#^}: Periorbital edema and erythema, most often of the upper eyelids and symmetrical. Figure 4. The cheeks, nasolabial folds and nose can be involved too.

When two or more of these signs are present, the diagnosis DM can be made (with additional skin biopsy).

Figure 3 Gottron’s papules on interphalangeal and metacarpophalangeal joints

Figure 4: heliotrope erythema of the face, extending to the periorbital region and upper eyelids

Common skin abnormalities compatible with dermatomyositis:

• Periungual changes^@: Figure 5. Periungual erythema, edema, telangiectasias, dystrophic cuticles, hemorrhagic nailfold infarcts.
• V-sign^$: Erythematous, confluent macules and patches over the lower anterior neck and upper chest. Figure 6. The skin may seem atrophic.
• Shawl sign^#: Violaceous or erythematous macules and patches over the back of the shoulders, neck, upper back and possible lateral arms. Poikiloderma (see below for description) may also be present in the same distribution.
• Holster sign: Symmetric poikiloderma of hips and lateral thighs below the trochanter major. Can be reticulated, livedoid, or linear.
• Scalp involvement: Atrophic, erythematous, sometimes pruritic scaly plaques. Alopecia. Mimicking psoriasis or eczema.

Figure 5 Periungual changes

Figure 6 V sign

Less common skin abnormalities compatible with dermatomyositis:

• Vesiculobullous, necrotic or ulcerative lesions^*, often associated with cutaneous vasculitis.
• Cutaneous vasculitis^%: Petechiae, palpable purpura, livedo reticularis, necrosis, erosions and ulceration.
• Calcinosis cutis^%: Superficial bony white papules or nodules, most commonly over bony surfaces or at sites of inflammation, especially elbows, knees and buttocks.
• Poikiloderma (atroficans vasculare)^#: Trias of hypo- or hyperpigmentation, telangiectasias, and atrophy, usually found on the upper chest and lateral arms.
• Periorbital swelling and facial swelling: Edema with or without erythema.

Uncommon cutaneous manifestations of dermatomyositis:

• “Mechanic’s hands” ^*&: Hyperkeratosis, scaling, and fissuring of the lateral parts of the fingers or palms.
• Deck chair sign: Erythematous eruptions sparing transverse skin folds. May be first cutaneous sign preceding classic DM skin findings.
• Panniculitis^*: Painful, indurated nodules of buttocks, arms, upper parts of the thighs, and abdomen. Longstanding panniculitis leads to lipodystrophy.
• Flagellate erythema^@: Linear erythematous macules and patches on the back.
• Mucinosis: Erythematous papules or plaques, often in a reticular pattern, and scleromyxedema.
• Follicular hyperkeratosis (Wong-type dermatomyositis): Follicular, hyperkeratotic papules on extensor surfaces resembling pityriasis rubra pilaris.
• Erythrodermia: widespread erythema.
• Oral mucosal changes: Variable, but gingival telangiectasias, erosions, ulcers, and leukoplakia-like lesions have been reported, as well as ovoid palatal patches ^($)

Common but non-specific abnormalities, compatible with dermatomyositis:

• Raynaud phenomenon: Episodic vasospasm in fingers or toes in response to cold with triphasic color change^&
• Palmar hyperkeratosis ^$
• Psoriasiform plaques ^$
• Atrophic hypopigmented patches with overlying telangiectasias ^$
• Painful palmar papules ^*
• Peripheral oedema ^{^% D}

Note that patients with skin of color will generally show less erythema, or no erythema at all. In a recent case series by Ezeofor (2023) of 14 adults with skin of color, dyschromia was the most prominent cutaneous feature noted (n=8), with patients demonstrating hypopigmentation, hyperpigmentation, and/or poikiloderma. Gottron papules were observed in five patients. Facial erythema was noted in three patients, four had V-neck erythema, and five had a positive shawl sign. Two patients demonstrated a classic heliotrope rash (though subtile), whereas another was found to have periorbital changes described as “hypopigmented patches with telangiectasias, and erythema”.

Skin changes with other forms of IIM

Skin changes similar to those in DM were reported in a Chinese population with anti-HMGCR IMNM. Out of 21 patients 9 exhibited DM-like skin changes, of which 1 showed a heliotrope rash and 2 showed Gottron’s sign. In the other cases, patients showed erythema and hypo- and hyperpigmentation on their cheeks, limbs, and both sides of the trunk (Hou, 2022). DM-like rashes were also reported in one other Asian populations (Kadoya, 2016)

Skin changes can also be observed in the anti-synthetase syndrome in which mechanic’s hands (Shinoda,2021; Gusdorf, 2019) and Raynaud phenomenon are part of the clinical spectrum (Marguerie, 1990). Describing skin changes of connective tissue disorders/myositis overlap syndromes is beyond the scope of this chapter.

Characteristics of the lungs

Interstitial lung disease (ILD) can present itself rapidly progressive, or following a slowly progressive course, or as an asymptomatic feature. Usual complaints are dyspnea on exertion, (dry) cough, and decreased tolerance to exercise. In DM, muscle disease usually precedes ILD, but this is not always the case. Rapidly progressive ILD is more common in CADM patients, especially in patients with MDA5 antibodies, and is associated with a higher mortality. Additionally, ILD is part of the ASS. In IMNM, ILD is rare and does not normally result in clinical symptoms or signs, and thus has no clinical implications (Allenbach, 2020).

Characteristics of the heart

Myocarditis is a well-known manifestation of IIM with uncertain prevalence. There is limited information on heart involvement in IIM, both due to the rarity of the diseases and because manifest cardiac complications in these patients are uncommon (Cheng, 2022; Fairley, 2021; Opinc, 2021; Zhang, 2012). In most of the literature, cardiac involvement in IIM has been demonstrated by ancillary investigations. Rhythm and conduction abnormalities are the most frequently reported cardiac abnormalities in patients with IIM. Cardiac abnormalities can also present with chest pain, palpitations, congestive heart failure, electrocardiographic or electrophysiologic abnormalities or MRI abnormalities.

Malignancies

Malignancies are found in adult patients with a recent diagnosis of IIM, with a Standardized Incidence Ratio (SIR) varying between 2.0-2.5 (for IIM in general) to 2.0-8.0 (for DM) (Tiniakou & Mammen, 2017). Cancer-associated myositis is defined as a malignancy occurring within 3 years before or after the diagnosis of IIM (Lilleker, 2018; Opinc, 2022; Kaneko, 2020). Associated malignancies can be either solid or hematological. In DM, lung and gastrointestinal tumors have been reported the most, but also ovarian, breast, prostate, kidney and nasopharynx tumors, with differences in prevalence between populations.

Malignancies have been described in 12 patients with JDM only up to date. These were mainly hematological of origin. These patients exhibited splenomegaly, lymphadenopathy or atypical rash (Morris, 2010). Malignancies and IBM or overlap myositis are not associated.

General symptoms and signs

Fever, malaise and weight loss are present in most patients with JDM. They can also be present in adult forms of IIM. Arthralgia, myalgia and fatigue are often mentioned in the presence of IIM, but exact prevalence numbers at case presentation were not found. Myalgia is not an obvious symptom in IBM.

Differential diagnosis

Below a differential diagnosis list for muscular and skin features is given for IIM, JDM or IBM. Please note that these are not comprehensive lists but meant as an aid to facilitate swift diagnosis.

Muscle:

• Subacute, more or less symmetrical proximal muscle weakness
  • Metabolic myopathies (hypothyroidism, hypoparathyroidism), sarcoidosis, infectious disorders (e.g. Lyme’s disease, pyomyositis, trichinellosis, toxoplasmosis), toxic (e.g. colchicine myopathy, amiodarone myopathy), sporadic late onset nemaline myopathy, subacute polyradiculopathies, chronic inflammatory demyelinating polyneuropathy (motor predominant), motor neuron disease, myasthenic syndromes, meningitis carcinomatosa, critical illness myopathy, other types of IIM (for example Graft versus host disease, eosinophilic myositis, immune checkpoint inhibitor associated myositis, CANDLE syndrome (chronic atypical neutrophilic dermatosis with lipodystrophy and elevated temperature).
  • Disorders in which proximal muscle weakness may be perceived as recently developed such as limb girdle muscular dystrophies, facioscapulohumeral dystrophy, Pompe disease and others.
• Slowly progressive muscle weakness with predominantly
  • Quadriceps involvement: Becker muscular dystrophy, limb girdle muscular dystrophy (anoctamin5, dysferlin), radiculopathies, femoral neuropathy, motor neuron disease, Lambert-Eaton myasthenic syndrome, steroid myopathy
  • asymmetric involvement: limb girdle muscular dystrophy (anoctamin5, caveolin, calpain, dysferlin, Duchenne female carriers), VCP/IBM-P-FTD myopathy, facioscapulohumeral muscular dystrophy, motor neuron disease, multifocal motor neuropathy, plexopathy, radiculopathy, mononeuropathy
  • finger flexor involvement: myotonic dystrophy, Becker muscular dystrophy, myofibrillar myopathy, sarcoid myopathy, amyloid myopathy, ACTA1-myopathy, GNE-myopathy, VCP-myopathy, limb girdle muscular dystrophies (dysferlin, LGMD-D3), Pompe’s disease, LAMA2-muscular dystrophy) (Nicolau, 2020).
  • weakness of oropharyngeal muscles: oculophayngeal muscular dystrophy, myotonic dystrophy, myasthenia gravis, motor neuron disease, sarcoid myopathy, facioscapulohumeral muscular dystrophy (Vivekanandam, 2020).

Skin:

Differential diagnosis of cutaneous lesions:

• Gottron’s papules: lichen planus, cutaneous lupus erythematodes, knuckle pads
• Gottron’s sign: psoriasis vulgaris
• Heliotrope erythema can also be mistaken for an (aerogenic) contact dermatitis
• Shawl sign/V-sign: sun burn, phototoxic reaction, photoallergic reaction, more diffuse chronic discoïd lupus erythematodes, foto(recall) dermatitis, radio(recall)dermatitis
• Holster sign: when reticulated or livedoid, it can also match with the diverse diseases that can cause a livoid vasculopathy (e.g., polyarteriitis nodosa, antiphospholipid syndrome)
• Scalp involvement can be misdiagnosed as seborrheic dermatitis, eczema or psoriasis
• Poikiloderma: Civatte poikiloderma (suninduced), radio(recall)dermatitis). Poikiloderma at the thighs and hips can be found in cutaneous T-cell lymphoma or mycosis fungoides.
• Periorbital oedema and facial swelling can be found in for example angioeodema or morbus Morbihan.
• The differential diagnosis of vasculitis is very broad.
• Calcinosis cutis can for example also be found in more sclerodermiformic dermatosis as an (post)inflammatory sign.
• Mechanic’s hands: (rhagadiform) hand eczema, keratoderma (also paraneoplastic), Bazex syndrome
• Flagellate erythema can be present in adult-onset Still’s disease, bleomycin-induced dermatitis, and shiitake dermatitis.
• Deck chair sign can also be found in Sezary’s syndrome (a form of cutaneous T-cell lymphoma)
• Folliculair hyperkeratosis can be found in pityriasis rubra pilaris, lichen spinulosis, follicular lichen planus or keratosis pilaris, however, it could also be a sign of folliculotropic mycosis fungoides
• The differential diagnosis of panniculitis is very broad.
• Erythroderma is very unspecific and can be observed in in a wide varity of dermatosis.
• The oral mucosal changes are very broad and the differential diagnosis falls beyond the scope of this guideline.

In children consider CANDLE and SAVI (STING-Associated Vasculopathy with onset in infancy) syndrome.

To answer the clinical question, an exploratory search was conducted into the symptoms and signs of IIM, including JDM and IBM. These signs and symptoms result from the history and findings of physical (including neurological) examinations.

Search and select (Methods)

The databases Medline (via OVID) and Embase (via Embase.com) were searched exploratory using relevant search terms until July 21^st, 2021. The detailed search strategy is depicted under the tab Methods. The exploratory literature search resulted in 699 hits. Systematic reviews and guidelines were assessed for usability, resulting in a first selection of 18 articles for full text assessment. After reading the full text, none of the articles were included due to limited description of individual clinical signs or symptoms. A table with reasons for exclusion is presented under the heading Evidence tables.

Results

Based on our review of the literature, the diagnostic value of distinct clinical features or patterns of disease presentation was not found to have been investigated systematically. Instead, a description of the most frequent and characteristic signs and disease patterns is given for IIM, including JDM and IBM, in particular those items that could discriminate between the different subtypes. The presence of these signs or patterns should aid the clinician to suspect one of the subtypes of the above-mentioned disorders. However, the suspicion on one or the other cannot be made without knowledge about the likelihood of the disorder based on age (at onset), incidence or prevalence in the population. The sequence in which signs of a disease present themselves and progress can vary between individuals.