Severe stiffness or catatonia
- Catatonic schizophrenia
- Parkinson's disease
- Catatonic syndrome due to other CNS causes, e.g., viral encephalitis, CNS bleed
- Neuroleptic-induced catatonia
- Seizure or status epilepticus
- Neuroleptic malignant syndrome
- Malignant hyperthermia
- Tetany, e.g., hypocalcemia (usually distal muscles)
- Dystonic reaction to neuroleptics, e.g., torticollis
- Huntington's disease
- Tetanus
- Strychnine poisoning
- Lethal catatonia
- Stiff-person syndrome
- Meningitis (stiff neck)
Mild stiffness
- Arthritis, e.g., osteoarthritis, rheumatoid arthritis, pseudogout
- Early parkinsonism
- Fibromyalgia
- Polymyalgia rheumatica