1st order laboratory parameters – obligatory laboratory tests.
- Small blood count
- Differential blood count
- Inflammatory parameters – CRP (C-reactive protein) or ESR (erythrocyte sedimentation rate).
- Creatine kinase (CK) (isoenzyme CK-MM) – the most important parameter in the detection of muscle diseases (polymyositis, dermatomyositis, but also in infectious myositis) Attention! Even in healthy individuals after heavy muscle work (e.g. bodybuilders, high-performance athletes or construction workers), after i.m. (intramuscular) injections, significantly elevated CK values are found (not infrequently up to 10 times the upper limit of the norm). In statin-treated patients should be discontinued at a CK increase above 4-5 times the norm or must be discontinued at a CK increase above 10 times the norm.
- Interpretation of elevated CK levels:
- CK > 10 times the upper norm → myopathy, myositis (clinical picture: often generalized pain; independent underlying muscle disease?).
- CK > 40-fold of upper norm → rhabdomyolysis/dissolution of striated muscle fibers/skeletal muscles as well as cardiac muscles (clinical picture: muscle symptoms with renal dysfunction and myoglobinuria (dark discolored urine)).
- Electrolytes – calcium, sodium, potassium, magnesium, phosphate.
- Urine status (rapid test for: nitrite, protein, hemoglobin, erythrocytes, leukocytes) incl. sediment, if necessary urine culture (pathogen detection and resistogram, that is, testing suitable antibiotics for sensitivity / resistance).
- Fasting glucose (fasting blood glucose).
Laboratory parameters 2nd order – depending on the results of the history, physical examination and the obligatory laboratory parameters – for differential diagnostic clarification.
- Myoglobin (muscle protein from the globin group).
- Vitamin D (25-OH vitamin D)
- Serological or bacteriological examination – if bacterial, viral or parasitic infections are suspected.
- Molecular genetic examination – if genetic diseases are suspected.
- Thyroid parameters – TSH, fT3, fT4
- Parathyroid function parameters – parathyroid hormone.
- Liver parameters – alanine aminotransferase (ALT, GPT), aspartate aminotransferase (AST, GOT), glutamate dehydrogenase (GLDH) and gamma-glutamyl transferase (gamma-GT, GGT), alkaline phosphatase, bilirubin – if chronic alcoholism is suspected.
- Rheumatism diagnostics – CRP (C-reactive protein) or ESR (blood sedimentation rate); rheumatoid factor (RF), CCP-AK (cyclic citrulline peptide antibodies), ANA (antinuclear antibodies).
- HMGCR (3-hydroxy-3-methylglutaryl-CoA reductase) – for suspected immune-mediated necrotizing myopathy (NM).
- Porphyrins
- Muscle biopsy – if muscular genesis is suspected* .
- Toxicological examination – in case of suspected intoxication (alcohol, heroin, cocaine).
- Porphyrins in urine – if porphyria is suspected.
- Carnitine and acetycarnitine determination in serum (with tandem mass spectrometry) – if a carnitine metabolic disorder is suspected.
- CSF puncture (collection of cerebrospinal fluid by puncture of the spinal canal) for CSF diagnosis – in suspected cases of poliomyelitis (polio), Guillain-Barré syndrome (GBS).
Further notes
- * For strain-related myalgias:
- Muscle biopsy is promising only if CK levels are elevated at least sevenfold.In nonstress-dependent myalgias and unremarkable neurologic findings, 2% of muscle biopsies are usually found to be nonspecifically abnormal.
- diagnostic value of a muscle biopsy increases when one or more of the following signs/symptoms are present:
- Myoglobinuria (excretion of myoglobin in the urine).
- “second wind” phenomenon (= affected person feels relief of symptoms after a short break and a reduction in exertion)
- Muscle weakness
- Muscle hypertrophy/atrophy
- CK: > 3-5-fold increased
- Changes of a myopathy (muscle disease) in electromyography (EMG; electrophysiological method in neurological diagnostics, in which the electrical muscle activity is measured and displayed on the basis of action currents of the muscles).
- Positive family history for the same complaints or neuromuscular disease.
