Spirulina and polymyositis: CD8+ T cell muscle infiltration, anti-Jo-1, ILD risk, prednisolone, and protein recovery

Polymyositis pathophysiology

CD8+ T cell-mediated muscle destruction: In polymyositis, CD8+ cytotoxic T cells directly invade muscle fibres expressing MHC class I (upregulated by IFN-γ in inflamed muscle). CD8+ T cells recognise muscle antigens in the context of MHC-I, release perforin/granzyme B, and cause muscle fibre necrosis. Unlike dermatomyositis, perivascular complement deposition and type I interferon signature are not prominent. NK cells are present in the muscle infiltrate but play a secondary role compared to CD8+ T cells.
NOX2 in muscle inflammation: Infiltrating macrophages and activated muscle fibres (under IFN-γ stimulation) express NOX2. ROS production contributes to bystander muscle damage independent of direct T cell killing. Phycocyanobilin’s NOX2 inhibition may reduce this oxidative amplification of muscle injury.
Anti-synthetase syndrome (anti-Jo-1): Anti-Jo-1 antibodies (targeting histidyl-tRNA synthetase) are the most common myositis-specific antibodies (~25% of inflammatory myopathies). Anti-synthetase syndrome: myositis + ILD + Raynaud’s + mechanic’s hands + arthritis. ILD can be progressive and is the most serious complication. Other anti-synthetase antibodies (anti-PL-7, anti-PL-12, anti-EJ) carry similar ILD risk. NK stimulation concern with active ILD: spirulina NK stimulation may worsen pulmonary inflammation — discuss with pulmonologist/rheumatologist.

NK cells play a secondary (not primary) role in polymyositis muscle infiltration, in contrast to dermatomyositis where NK cells are primary effectors. The NK stimulation concern in polymyositis is intermediate — lower than dermatomyositis but not absent. In active polymyositis: discuss with rheumatologist before starting spirulina. In anti-Jo-1 positive polymyositis with ILD: NK concern is higher (pulmonary NK cell activity contributes to ILD progression).

Muscle recovery in inflammatory myopathy requires adequate protein for sarcomere regeneration. Inflammatory myopathy itself causes protein catabolism (IFN-γ/TNF-α increase muscle protein breakdown); high-dose prednisolone adds corticosteroid-induced myopathy and protein catabolism on top of the inflammatory damage. Protein targets of 1.2–1.6 g/kg/day are recommended in inflammatory myopathy during active disease and recovery. Spirulina (3.5 g/5 g protein, complete amino acid profile) contributes to daily protein targets. At 5–10 g spirulina: approximately 3.5–7 g protein contribution to the daily target.
Leucine threshold: muscle protein synthesis (mTOR activation) requires leucine ≥2.5 g per meal. Spirulina leucine (~0.3 g/5 g) does not reach this threshold alone; spirulina should be used as a protein supplement alongside complete meal protein (meat, fish, eggs, legumes), not as the primary muscle-building protein source in inflammatory myopathy recovery.

Creatine kinase (CK) is the primary biomarker of muscle inflammation in polymyositis. Spirulina has antioxidant effects that may modestly reduce exercise-induced or inflammatory CK elevation. Some clinical studies in athletes show reduced CK after spirulina supplementation. Whether this extends to inflammatory myopathy is unknown. Do not interpret reduced CK as evidence of reduced disease activity without clinical correlation and specialist assessment.

High-dose prednisolone (1 mg/kg/day, often 40–80 mg/day) in active polymyositis. No pharmacokinetic interaction with spirulina. NK stimulation concern at immunosuppressive doses. Steroid-induced myopathy adds to inflammatory myopathy — protein adequacy and resistance exercise are the most important mitigation strategies.

IVIG used in refractory polymyositis and anti-synthetase ILD. No pharmacokinetic interaction with spirulina. As with dermatomyositis: IVIG infusion period and the week following are not the time to introduce spirulina; discuss timing with specialist.

Standard steroid-sparing agents in polymyositis. No pharmacokinetic interaction with spirulina. Intermediate NK concern; discuss with rheumatologist.

MMF used for anti-synthetase ILD management. No pharmacokinetic interaction with spirulina. Intermediate to high NK concern in active ILD context; discuss with pulmonologist.

Active polymyositis: intermediate NK concern (CD8+ primary, NK secondary); discuss with rheumatologist before starting
Anti-Jo-1 positive with ILD: higher NK concern; defer until specialist approval
Polymyositis in remission, off or on low-dose maintenance prednisolone (≤7.5 mg/day): NK concern lower; 1–2 g/day starting dose; monitor CK at next review
Protein target: 1.2–1.6 g/kg/day; spirulina contributes 3.5–7 g/5–10 g dose; ensure dietary protein meets leucine threshold per meal for mTOR activation
Report any new respiratory symptoms (dyspnoea, dry cough) to prescribing physician — ILD can develop or progress during treatment