Muscle weakness

True muscle weakness — reduced ability to generate force when you try — must be separated from fatigue (decreased endurance with preserved peak strength) and from feeling weak as a synonym for tired. The pattern matters: proximal weakness (difficulty rising from a chair, climbing stairs, raising arms above the head) suggests myopathy or endocrine cause; distal weakness (gripping, foot drop) suggests neuropathy; fluctuating weakness that worsens with use is myasthenia gravis. Important treatable causes: electrolyte disturbance (low potassium, low calcium, low magnesium, low sodium, low phosphate), hypothyroidism (proximal), hyperparathyroidism, hypercortisolism, vitamin D deficiency (proximal), statins and other myotoxic drugs, chronic kidney disease (uraemic myopathy), inflammatory myopathies (dermatomyositis, polymyositis), and motor neurone disease.

• Hypokalaemia, hypocalcaemia, hypomagnesaemia, hyponatraemia — sudden onset; check on first presentation.
• Hypothyroidism — proximal weakness + slow reflexes + fatigue.
• Vitamin D deficiency — proximal weakness, especially elderly and dark-skinned.
• Statin myopathy — calf aches + weakness; check CK.
• Chronic kidney disease (uraemic myopathy) — proximal weakness + raised creatinine.
• Cushing's, steroid use — proximal weakness + central obesity + skin changes.
• Polymyositis / dermatomyositis — high CK + skin rash + autoimmune workup.
• Myasthenia gravis — fluctuating + worse with exertion + diplopia / ptosis.
• Motor neurone disease — progressive, often asymmetric, fasciculations.

First-line panel: electrolytes (K, Na, Ca, Mg, phosphate), TSH and free T4, vitamin D, CK (creatine kinase), creatinine + eGFR. Add cortisol if Cushing's is suspected; ANA + anti-Jo-1 if inflammatory myopathy is on the differential; acetylcholine receptor antibodies if fluctuating + ocular. Mediora.AI surfaces electrolyte clusters and CK trends; rapid-onset or progressive weakness is a neurological emergency.