mononeuropathy is a form of peripheral neuropathy characterized by isolated damage to a single peripheral nerve, causing focal deficits in the distribution of that specific nerve. It is distinguished from polyneuropathy, which affects multiple nerves in a symmetric, length-dependent pattern, and from mononeuritis multiplex, which involves two or more separate, noncontiguous nerves in an asynchronous, multifocal pattern. The underlying pathophysiology typically involves mechanical compression, entrapment, or local ischemia that produces focal demyelination and, with sustained injury, secondary axonal degeneration. Mononeuropathy may be physiological (e.g., transient “sleep palsy” from prolonged pressure) or pathological (e.g., entrapment neuropathy such as carpal tunnel syndrome, traumatic nerve laceration, or vasculitic nerve infarction). Clinically relevant subtypes most commonly encountered in coding include carpal tunnel syndrome (G56.0x), ulnar nerve lesion (G56.2x), radial nerve lesion (G56.3x), sciatic nerve lesion (G57.0x), meralgia paresthetica (G57.1x), femoral nerve lesion (G57.2x), peroneal/lateral popliteal nerve lesion (G57.3x), and tarsal tunnel syndrome (G57.5x). A final distinguishing point: mononeuropathy should not be confused with radiculopathy, which involves the nerve root rather than the peripheral nerve itself and typically presents with dermatomal/myotomal patterns originating from the spine.
The word entered English in the 19th century as mononeuropathy (noun), formed within modern medical Latin/Greek from mono- + neuropathy, itself borrowed via French névropathie from Late Latin neuropathia, from Greek neuron + -patheia — literally “single-nerve disease.” The root neuro- (“nerve”) connects mononeuropathy to the entire -neuro- family: polyneuropathy (poly- + neuron + -pathy → “many-nerve disease”), neuropathy (neuron + -pathy → “nerve disease”), and neurology (neuron + -logia → “study of nerves”). The prefix mono- is highly productive in medical terminology: monocyte, monocular, monoplegia, monosomy, monaural.
polyneuropathy — the symmetric, length-dependent counterpart; involves many peripheral nerves simultaneously, typically in a stocking-glove distribution, usually from metabolic/toxic causes
mononeuritis multiplex — shares the mono- + neuro- roots; a painful, asymmetric, asynchronous neuropathy involving ≥2 separate noncontiguous nerve areas, often vasculitic; multifocal variant that may initially present as sequential mononeuropathies before confluent involvement (G58.7)
carpal tunnel syndrome — the single most common mononeuropathy; median nerve entrapment at the wrist (G56.0x)
nerve compression — the primary mechanical mechanism causing intraneural ischemia, venous congestion, and focal demyelination in entrapment mononeuropathies
neurapraxia — the mildest grade of nerve injury in Seddon’s classification; focal conduction block with intact axon, typically from compression
axonotmesis — more severe nerve injury with axonal disruption but preserved connective tissue sheath; Wallerian degeneration occurs distally
tardy ulnar palsy — delayed-onset ulnar nerve lesion, often years after elbow fracture; classic mononeuropathy (G56.2x)
meralgia paresthetica — lateral femoral cutaneous nerve entrapment at the inguinal ligament; pure sensory mononeuropathy (G57.1x)
diabetic mononeuropathy — focal nerve damage in diabetes, often cranial nerves or femoral nerve; G59.0
electromyography (EMG) — primary diagnostic tool for evaluating mononeuropathy; identifies denervation, localizes the lesion, and distinguishes axonal from demyelinating pathology
nerve conduction studies (NCS) — companion diagnostic procedure measuring conduction velocity and amplitude across the affected nerve segment
CODING CORNER
🏥 ICD-10-CM CODES
Mononeuropathies of Upper Limb (G56 — Laterality Required)
⚠️ Coding Note: All G56 and G57 codes require laterality specification — the 5th digit identifies right (1), left (2), or bilateral (3) involvement; unspecified codes (ending in 0) should be avoided when documentation supports specificity. When mononeuropathy is secondary to an underlying disease (e.g., diabetes), code the underlying condition first (e.g., E11.41 for Type 2 diabetes with diabetic mononeuropathy), followed by G59.0. An undercoding alert applies to G58.7 (mononeuritis multiplex), which is commonly missed when documentation uses vague phrases like “multifocal neuropathy,” “asymmetric nerve involvement,” or “sequential nerve palsies” — these should trigger a query for clarification. When electrodiagnostic studies (EMG/NCS) are performed on the same date of service as surgical decompression, modifier -25 should be appended to the E/M code and modifier -59 may be needed for the diagnostic study if performed in a distinct session. For nerve conduction studies, code selection (95907-95913) is based strictly on the total number of individual studies performed, not the number of nerves tested — each study type (motor, sensory, F-wave, H-reflex) counts separately.
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