M63.839 Disorders of muscle in diseases classified elsewhere, unspecified forearm

Billable ICD-10-CM code, FY2026.

Applies from M63 Disorders of muscle in diseases classified elsewhere

Excludes1 (never code together)

• myopathy in cysticercosis (B69.81)
• myopathy in endocrine diseases (G73.7)
• myopathy in metabolic diseases (G73.7)
• myopathy in sarcoidosis (D86.87)
• myopathy in secondary syphilis (A51.49)
• myopathy in syphilis (late) (A52.78)
• myopathy in toxoplasmosis (B58.82)
• myopathy in tuberculosis (A18.09)

Code first

• underlying disease, such as:
• leprosy (A30.-)
• neoplasm (C49.-, C79.89, D21.-, D48.1-)
• schistosomiasis (B65.-)
• trichinellosis (B75)

MS-DRG index

Defines the logic of DRG(s) 557-558 in MDC 08.

Approximate ICD-9-CM (GEMs)

• 728.9 Unspecified disorder of muscle, ligament, and fascia (approximate)

Medicare Code Edits (MCE v43.1 (April 2026))

• Manifestation codes as principal diagnosis: Manifestation codes describe the manifestation of an underlying disease, not the disease itself, and are not allowed as principal diagnosis.

Nearby codes

• M63.822 Disorders of muscle in diseases classified elsewhere, left upper arm
• M63.829 Disorders of muscle in diseases classified elsewhere, unspecified upper arm
• M63.83 Disorders of muscle in diseases classified elsewhere, forearm
• M63.831 Disorders of muscle in diseases classified elsewhere, right forearm
• M63.832 Disorders of muscle in diseases classified elsewhere, left forearm
• M63.839 Disorders of muscle in diseases classified elsewhere, unspecified forearm (this code)
• M63.84 Disorders of muscle in diseases classified elsewhere, hand
• M63.841 Disorders of muscle in diseases classified elsewhere, right hand
• M63.842 Disorders of muscle in diseases classified elsewhere, left hand
• M63.849 Disorders of muscle in diseases classified elsewhere, unspecified hand
• M63.85 Disorders of muscle in diseases classified elsewhere, thigh